30-Drop
A mode of the  REF _Ref43013674 \h SMPTE time code designed to allow synchronization of audio with U.S. NTSC color television material.  A quirk in the NTSC color standards, as implemented in the U.S., is that the frame rate is not exactly 30 frames/second; rather, it is slightly less, on the order of 29.97 frames/second.  Since the SMPTE standard doesn’t allow for a frame rate that isn’t an integral number of frames per second, this mode approximates the true rate by running at 30 frames/second, but with certain specified seconds throughout each hour having only 28 or 29 frames, so that the average stays close to the true NTSC color frame rate.  
30-Nondrop
The “standard” NTSC frame mode in the  REF _Ref43013674 \h SMPTE time code standard, which runs at a true and constant 30 frames/second.  It synchronizes with black-and-white NTSC television signals, but not with color signals; see  REF _Ref43013988 \h 30-Drop.
Active Sensing
A  REF _Ref35841199 \h MIDI message which provides a crude method of monitoring the integrity of a MIDI connection.  The transmitter sends the Active Sensing message approximately every 0.2 seconds.  If the receiver does not receive an Active Sensing message for about 0.5 seconds, it assumes that some break in the connection has occurred, and it acts as if an  REF _Ref38091154 \h All Notes Off message had been sent. to eliminate any possibility of  REF _Ref41740942 \h Stuck Notes.  In reality, this doesn’t work very well, and MIDI interfaces are often configured by default to filter the Active Sensing messages out.
A/D Converter
An electrical circuit that converts the instantaneous level of an analog signal into a numeric value.  By doing repeated conversions at a rapid rate, the converter can build up a digital representation of the input waveform.
Additive Synthesis
The creation of complex waveforms by adding together component sine waves; the inverse (conceptually) of a  REF _Ref35840291 \h Fourier Transform.  Additive synthesis can theoretically produce any possible waveform, but in practice it is difficult to design and work with.  Additive synthesis is impractical to implement with analog circuitry; it can be performed digitally but the amount of computing power needed is considerable.  So until the fairly recently, only those with access to large mainframe computer installations could experiment with additive synthesis.  In the mid-70s, the Synergy digital computer brought additive synthesis to the upper-end keyboard market, but it never caught on commercially.  Only a few other mass-market synths have been produced since which support additive synthesis, the best known of which are the Kawai K5 and K5000 series.
Adobe Premiere
A  REF _Ref41467112 \h Plug-In format for software-based effects.  As the name suggests, the format was developed by the Adobe company, and made its way into music from the video/film editing and post-production world.  This format does not support real-time processing, and so it has never gained wide popularity in the music world.
ADSR
The most common type of  REF _Ref42917501 \h Envelope Generator, producing a four-segment signal corresponding to four phases of a note’s dynamics (in the usual case where the signal is used to control a  REF _Ref42917711 \h VCA that determines the note’s volume).  Each letter of the acronym stands for one of the four phases, in time order:  REF _Ref42917886 \h Attack,  REF _Ref42917902 \h Decay,  REF _Ref42917917 \h Sustain, and  REF _Ref42917936 \h Release.
Aftertouch
A feature of many keyboards where the performer can generate a control signal by varying the amount of force applied to the keyboard while holding down one or more notes.  Aftertouch divides into two categories, channel aftertouch (referred to in the  REF _Ref35841199 \h MIDI standard as “channel pressure”) and polyphonic aftertouch (referred to in the MIDI standard as “key pressure”).  
Aliasing

All Notes Off
A  REF _Ref35841199 \h MIDI message that, when received, instructs the receiver to release all notes that are currently being sounded.  It is commonly used to get rid of stuck notes resulting from missed MIDI messages or software problems.  Note that it does not mean that the receiver should go silent immediately!  It is the equivalent of sending a Note Off message for all notes which are currently sustaining; if the current patch is programmed with a long envelope release time, the notes may continue to sound for some time.  
Allpass Filter
A  REF _Ref36446120 \h Filter whose cutoff is set just outside the audio range, so that all audio-frequency signals pass through (perhaps with some attenuation at the extremes).  Such a circuit is used for a side effect of the filter circuit, that being its property of shifting the phase of the output signal at an angle which is proportional to the input frequency.  Mixing the output with the unmodified input signal results in the effect known as “phasing”.  See phaser.  
Amplitude Modulation
A variation in the amplitude of a carrier signal, according to the instantaneous value of a modulating waveform.  When the modulation is of subsonic frequency, the result is a slow or rapid variation in the volume level of the carrier signal which is referred to as “tremolo”.  When the modulation is of audio frequency, the result is a composite waveform containing components at sum and difference frequencies of the partials of the carrier and the modulation.  These frequencies are often not harmonically related to the carrier, and the results can be bizarre.  See also  REF _Ref36143630 \h Ring Modulation.  Compare with  REF _Ref36143656 \h Frequency Modulation.  For some reason, audio-frequency AM is seldom implemented on commercial synths.  
Analog
An electrical circuit which represents quantities within the circuit as signals with continuously variable voltages, the voltage encoding the value of whatever quantity the circuit deals with.  Compare with Digital.
Analog Synthesizer
One which employs all analog circuits, at least in the audio signal path.  
Arpeggiator

ASIO
A standard for  REF _Ref41467021 \h Audio Interface software drivers and programs that do audio recording.  The ASIO standard provides a standard interface to audio recording programs (and  REF _Ref38201901 \h Sequencer programs that do  REF _Ref41743334 \h Hard Disk Recording) so that they don’t have to have separate software for each different model of audio interface hardware; it also provides useful capabilities for minimizing timing variations.  As of this writing, ASIO is the most popular standard for both the PC and Mac platforms, but the Mac OSX operating system is attempting to replace it with  REF _Ref41743401 \h Core Audio.

Attack

Audio Interface

Audio Units
A  REF _Ref41467112 \h Plug-In standard included by Apple in its OSX operating system.  Audio Units is intended to replace manufacturer-specific plug-in standards like .  In theory, all  REF _Ref38201901 \h Sequencer software and plug-ins written for OSX will support this standard, and plug-in authors will no longer have to write multiple versions for different standards.  
Auto Tune
A function of some  REF _Ref39424455 \h Analog Synthesizers that automatically tunes the  REF _Ref38088628 \h Oscillators (and, in better implementations, the  REF _Ref36446120 \h Filters too) using a built-in frequency reference.  As it turned out, the technology advances that made this practical also resulted in the development of the  REF _Ref41742351 \h DCO, which does not need frequent tuning, so only a few synth models designed in the late ‘70s-early ‘80s period ended up with an auto tune function.  
Bandpass Filter
Bank Select
A  REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller message that uses controller type 0 (and optionally type 32 to extend the range of available values) to extend the range of the  REF _Ref39471498 \h Program Change message.  When the MIDI standard was first drawn up, memory was expensive, and the creators of the Program Change message assumed that the 128 possible  REF _Ref38090765 \h Patch numbers was more than any practical synth would ever have memory for, due to cost considerations.  However, with memory having become far cheaper since 1980, many synths now have more than 128 patch storage locations.  To extend the range of patch numbers, the MIDI standard allows patches to be grouped into “banks” of 128 patches; the Bank Select message selects a bank of patches, and then the Program Change message selects a patch within the back.  Unfortunately, some manufacturers started using the Bank Select controller type before it was officially added to the MIDI standard, and so some early-1990s synths can be found which don’t do Bank Select properly because, although they recognize the message, they require a non-standard format.  Some  REF _Ref38201901 \h Sequencers have the ability to generate Bank Select messages in different formats to accommodate this.  
Bass Pedals
A synth specialized to produce bass sounds, and played with the feet, in the manner of organ pedals.  (Some are arranged so that a performer who plays standing up, such as a guitarist, can play the pedals with one foot while standing on the other foot.)  By far the best known example is the 1970s Moog Taurus, which contained a simple  REF _Ref39424455 \h Analog Synthesizer tuned for bass notes, connected to a 1-1/2 octave pedalboard and foot-operated controls for selecting preset sounds or a programmed sound (set up by programming controls hid from wayward footsteps under a cover).  Nowdays, it is more common to find pedalboards that generate  REF _Ref35841199 \h MIDI messages for controlling an external synth.
BBD

Breath Controller
(1) A device that generates a control signal corresponding to how hard the performer blows into it.  Some such devices may also have “valves” connected to switches to generate additional control signals, serving as an alternate to a  REF _Ref38203151 \h Master Keyboard for woodwind or brass players.  (2) A  REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller message, type ???, which is intended to correspond to the output of a breath or pressure sensor.  The sound parameter that this controller message is supposed to control isn’t specified by the standard; most synths that accept this message use it control either main volume or a  REF _Ref36446120 \h Filter setting.
Cassette Interface
A mechanism used in 1980s-era synths to provide for external storage of  REF _Ref38090765 \h Patch data, prior to the availability of low-cost disk drives (it was also common on personal computers of the era).  To use the interface, the user connected the synth’s cassette interface to an ordinary audio cassette deck.  To store patches, the user put the cassette deck into record and then pressed a “SAVE” button on the synth; the synth then encoded the patch data into an encoded audio signal (using techniques similar to a computer modem) and sent it to the cassette deck to be recorded.  To reload the patches, the user pressed the “LOAD” button on the synth and then set the cassette deck to play; the synth received the audio signal and decoded the patch data from it. (Some units also had a “VERIFY” function that checked the tape after a save by reading back the saved data and comparing it to the data in memory.)  Cassette interfaces were always slow and not very reliable, and they disappeared as soon as reasonably priced floppy disk drives became available, around 1987.
Channel
In  REF _Ref35841199 \h MIDI, a logical division of a physical transmission cable, somewhat analogous to the way that a cable TV system carries multiple program channels on one cable.  The MIDI standard divides each cable into 16 logical channels.  In the early days of MIDI, before multitimbral synths existed, most synths that received MIDI data received only on a single channel (unless in Omni mode).  Keyboard cable of setting up splits could then be programmed to transmit on different channels to control multiple synths from different regions of the keyboard.  When multitimbral synths arrived, the concept was extended so that (in most cases) the transmitting MIDI device sees the receiving device as a number of synths in one box, each capable of playing a different  REF _Ref38090765 \h Patch under control of a different channel.  (Originally, the MIDI standard envisioned multiple channels being used to allow separate control of each voice in a  REF _Ref38124932 \h Polyphonic synth, but this has seldom been implemented.)
Channel Aftertouch
An  REF _Ref38125013 \h Aftertouch signal which is proportional to the average or total force being applied to the whole keyboard and equally effects every note being played.  In the  REF _Ref35841199 \h MIDI standard, the message that transmits this information is called “channel pressure”.  Compare with  REF _Ref38125448 \h Polyphonic Aftertouch.  
Clock

Comb Filter
A filter consisting of a series of notches (as in a  REF _Ref39425405 \h Notch Filter) in a regular repeating sequence.  Such filters produce a characteristic modification of an input audio signal, resulting in a sound similar to what might result if one were to listen with a long cardboard tube placed to one’s ear.  Comb filters are seldom produced using discrete notch filters for each notch; the easy way to do such filtering is to either delay the input signal or alter its phase, and then mix this in some proportion with the original signal.  If such a filter is varied over time, so that the notches move up and down the frequency spectrum as a group, an effect known as Flanging or Phasing results.  
Controller
(1) A device which generates a signal which is intended to control a sound generation or modifying component of a synth.  (2) A keyboard which lacks any sound generation circuitry of its own; it plays external synths by means of transmitting  REF _Ref35841199 \h MIDI messages.  (3) A type of  REF _Ref35841199 \h MIDI message which is intended to control parameters of synth sound production other than turning notes on/off; usually this message type corresponds to the operation by the performer of some auxiliary performance control device such as a control knob, a footswitch, or an expression pedal.  The MIDI standard allows for 121 possible types of controller messages, some of which are assigned to standard meanings; for instance, controller 1 is assigned to Modulation, which is usually generated by the mod wheel on a keyboard and conventionally is used to add vibrato to a produced sound.  (Unfortunately, the standard is not very consistent about the meanings of some of the standard assignments.  For instance, some such as Main Volume and Pan derive their names from the functions they are intended to perform, while others such as Breath Controller and Data Entry are named after the types of input devices that generally produce controller messages of that type.)
Control Surface
A device that generates  REF _Ref35841199 \h MIDI messages for controlling audio mixing software on a computer, as an alternative to using the computer mouse and keyboard.  Conventionally, the control surface duplicates the layout and general feel of a traditional mixing desk, but instead of containing actual mixing circuits, the control surface sends MIDI messages that the software recognizes for control of the mixing fuctions.
Control Voltage
A signal intended to control some other parameter, such that the value of that parameter corresponds to the voltage.  For instance, a  REF _Ref43560875 \h VCO might have a control voltage input which sets its frequency.  In a well-designed  REF _Ref39424455 \h Analog Synthesizer, control voltages and audio signals are interchangeable, such that, for instance, the output of a VCO could be used as a control voltage input to some other parameter.  
Core Audio
The basic set of audio signal-handling libraries and drivers bundled with Apple’s OSX operating system. This software set is intended to replace earlier standards like  REF _Ref41466960 \h ASIO and device-specific drivers with a universal software interface that will (in theory) work with all types of  REF _Ref41467021 \h Audio Interface connected to an Apple computer.   Not to be confused with  REF _Ref41467045 \h Audio Units, also found in OSX but which serves a different purpose.
Cross Modulation

Csound
A programming language designed specifically for constructing  REF _Ref39587487 \h Soft Synths, and the software that implements it.  Evolved from the groundbreaking MUSIC I-V programs developed at Bell Labs in the 1960s, the package is currently available through MIT Press.  Csound contains built-in algorithms for generating and modifying signals in various ways, and it allows the programmer to implement arbitrary algorithms to manipulate digital signals down to the individual word level.  An extremely powerful package, but academically oriented and not really commercially marketed (MIT Press charges just enough to cover its costs), Csound has only minimal user interfaces and requires some dedication to learn well enough to be usable.  
Curtis

Cutoff Frequency
The frequency where a low-pass or high-pass  REF _Ref36446120 \h Filter begins to filter out the signal.  By convention, the cutoff frequency is given as being the point where the output signal level is attenuated by 3 dB below the input signal.  The frequency where the filter effectively eliminates the signal will be past this; how far past depends on the slope and response curve of the filter.  
CV/Gate

D/A Converter

DCO
An acronym for “digitally controlled  REF _Ref38088628 \h Oscillator”.  Use of this term is somewhat vague; it can refer to either of two oscillator designs: (1) An oscillator circuit that outputs an analog signal, but is controlled by a digital control signal.  Such an oscillator has the virtue that it stays in tune, unlike an all-analog  REF _Ref43560875 \h VCO circuit.  (2) An oscillator that reproduces a signal stored digitally in memory by means of reading individual signal value words from the memory and setting a  REF _Ref43560964 \h D/A Converter to the indicated value, repeatedly and very fast, such that a cyclic signal is reproduced.  Unlike the previous example, this is an all-digital circuit.  This circuit is integral to  REF _Ref43561039 \h Wavetable Synthesis.
Data Entry

Decay
The portion of a conventional  REF _Ref42917650 \h ADSR  REF _Ref39565833 \h Envelope which occurs immediately after the  REF _Ref42917886 \h Attack.  The decay simulates the property of many acoustic instruments of decreasing in volume after the initial attack down to a constant  REF _Ref42917917 \h Sustain level.  Some types of instruments, notably organs, have no decay to speak of.  The term can also refer to a “sustain decay” in which the volume gradually drops during the sustain phase (many Yamaha synths implement this), used to simulate percussive tuned instruments such as pianos and bells (this is not part of a standard ADSR envelope).  
Delay Line
An electronic circuit which delays the passage of a signal through it, such that any given signal that is applied to the input will appear at the output after a precise amount of time has elapsed.  
Delta Modulation
A method of digitally compressing an input signal.  In delta modulation, the incoming signal is first converted to digital form by an  REF _Ref43018218 \h A/D Converter, if necessary.  For each word of data produced by the A/D converter, a processor encodes the mathematical difference between that word and the previous word; this difference value is what is stored or transmitted, with the original A/D output being discarded.  To reproduce the signal, the first stored word is read and output.  Then the second stored word is added to that value, forming the value that is to be output.  Each subsequent stored word is added to the accumulated total to form the next word value to be output.  A delta-modulated signal can be stored in less memory than the original signal; it was heavily used in the early digital  REF _Ref43561364 \h Delay Line designs in the 1970s and 80s because memory was so expensive then.  However, delta modulation has great difficulty handling signals which change rapidly; transients can drive it into a form of  REF _Ref43561468 \h Aliasing distortion.  Delta modulation was abandoned in the 1990s when memory became much cheaper.  (One interesting use of the technique remains: it is used to encode the space-to-ground voice transmissions from the Space Shuttle.)
Drop Frame
Drum Machine
A synth specially designed to produce drum sounds, and usually incorporating a  REF _Ref38201901 \h Sequencer capable of producing combinations of typical drum patterns (repeating sequences of usually 4 or 8 bars of drumming, programmed in the manner in which a drummer might play a certain style of music).  
DSP

Effect
A device that alters an incoming audio signal in a way that is considered musically interesting.  (Devices that alter the signal to assist the recording process are not usually considered effects as such.)  Originally the term referred exclusively to hardware devices that were designed specifically to generate effects.  However, today many synths have effects built-in, and it is also common to find them implemented as software  REF _Ref41467112 \h Plug-Ins for  REF _Ref38201901 \h Sequencer programs.  
Envelope
The average volume level of an audio signal, or a control signal representing the volume level.  
Envelope Follower
An electronic circuit which produces a control signal proportional to the  REF _Ref39565833 \h Envelope of an input signal.  Such a device is most commonly used for allowing a synth to track the dynamics of a conventional instrument, such as a guitar or a piano.  
Envelope Generator
A circuit which generates a signal, usually meant to control a  REF _Ref38202304 \h Voltage-Controlled Amplifier for the purpose of giving dynamics to a sound (in order words, providing a rise and fall of the volume of the note).  A typical envelope generator produces a signal which, as seen on an oscilloscope, appears as a series of line segments.  Controls are provided for setting the quickness or slowness of the rise or fall of the segments.  The most common type of envelope generator is known as an “ADSR” generator, which is designed to produce envelopes that can simulate the dynamic characteristics of many acoustic instruments.  The ADSR envelope generator has four segments known as “attack”, “decay”, “sustain”, and “release” (hence the acronym).  The segments occur in that order in time.  The attack segment starts when the key is pressed; itprovides an initial upward spike from the zero level.  The decay immediately follows the attack; this is a descending segment intended to provide a drop in volume after the attack.  The sustain is a level phase, and typically the envelope generator is wired such that the sustain lasts as long as the key is held down.  The release phase begins after the key is released; it takes the sound back to zero level.  More advanced envelope generators provide more segments, allowing more complicated volume envelopes to be produced; the ultimate in this area can be seen in some of the newer  REF _Ref39587487 \h Soft Synths which provide envelope generators with hundreds of segments.  In addition to volume, envelope generators are often used to produce  REF _Ref39587552 \h Pitch and  REF _Ref36446120 \h Filter variations.  
Exponential Amplifier
A type of amplifier circuit used in some  REF _Ref39424455 \h Analog Synthesizers to process  REF _Ref54081149 \h Control Voltage inputs to  REF _Ref38091874 \h Voltage-Controlled Oscillators,  REF _Ref38202333 \h Voltage-Controlled Filters, and other pitch-specific processing functions.  The nature of most VCO and VCF circuits is that they respond to their control voltage input in a “linear” fashion (from an electrical engineering standpoint); that is, they have a  REF _Ref54081407 \h Volts/Hz response to the control voltage.  Because  REF _Ref54081464 \h Volts/Octave response is preferred by many performers and is usually easier to deal with when mixing control voltages, the exponential amp circuit is used to pre-process the inputs to the VCOs and VCFs to get the desired respose.  The exponential amp, as the name might suggest, produces an output voltage that is exponentially proportional to the input voltage.  (The typical amplifier produces an output voltage which is the input voltage multiplied by a constant gain factor.)  Analog exponential amplifiers that track accurately are rather difficult to design and build, and in some older analog synths these circuits rely on components which were produced in the 1970s and are rare now.
Expression Pedal

Factory Preset
A  REF _Ref38090765 \h Patch pre-loaded into the memory of  a synthesizer by the manufacturer.  The patch may be loaded into  REF _Ref42935370 \h RAM, where it can be edited or overwritten by the user (this method was often used in the ‘80s), or into  REF _Ref72914985 \h ROM where it is always present and can’t be edited without copying it to a RAM location first.  The purpose of factory patches is two-fold.  First, they provide a starting point for new users, and a set of templates containing useful default settings for given types of patches.  Second, they provide a “wow” factor for the user playing the synth at the music store, and help to market the synth towards keyboard players who do not do their own programming.  (As an extreme example, the Yamaha DK7 powered up to a default electric-piano patch, and many people who purchased the synth used it solely for these purpose ⎯ never selecting any other patches, much less doing any editing.)  Factory patches can be useful starting points, but they can also be crutches for lazy performers, and so they get a certain amount of disdain from the hard-core synth community.  
Fast Fourier Transform
An algorithm for computing a  REF _Ref35840291 \h Fourier Transform in a way that is practical to compute on a personal computer or workstation.  The algorithm works by processing a group of samples representing a short period of time of the waveform being transformed; therefore, the output of the transform represents the average frequency content over the period of time being sampled.  A tradeoff that the implementer must make is deciding on the length of the time period being sampled; shorter periods of time produce a more instantaneous view of the waveform, but the resulting analysis has less resolution than an FFT performed on a longer sample.
Feedback

Filter
An electronic circuit that eliminates a selected range of frequency components from a signal.  
Firewire
A very high speed serial interface (much faster than  REF _Ref43018246 \h USB).  Firewire is an Apple trademark for their implementation of the IEEE 1394 standard (which they developed), and all newer Macintosh computers (G3- and G4-based) include it as standard equipment; it is also beginning to appear in some Wintel platforms, and PCI-based Firewire add-on cards are widely available.  In electronic music, Firewire is rapidly becoming the interface of choice for audio I/O by Mac users; several companies have developed  REF _Ref41467021 \h Audio Interfaces containing  REF _Ref43018218 \h A/D Converters with a Firewire ouput.
Flanging
An effect that results from delaying an input signal for a short amount of time (a few milliseconds) and then mixing the delayed signal with the original signal.  This creates a  REF _Ref39505873 \h Comb Filter with harmonically related notch frequencies.  If the delay time is varied, the notch filter sweeps back and forth, resulting in a distinctive “whooshing” or “jet plane” effect.  The name “flanging” comes from the technique originally used to produce the effect in the 1960s; two tape machines were set up to record the same signal, and the engineer produced the effect by pressing on the flange of the supply reel on one tape unit to slow it down (hence delaying the signal) relative to the other one.  (This method of producing the effect is now known as “tape flanging” and is seldom done nowadays, although it does produce a somewhat different sound than the more common technique which employs a delay line.)  
Flash Memory
A type of memory that is non-volatile (capable of retaining its contents when power is removed).  In music synthesizers, flash memory is often used in memory cards that provide external patch or waveform storage; compared to floppy or removable disks, they have the virtue of having no moving parts and being immune to magnetic fields.  Early types of flash memory could only be written to a limited number of times, but newer designs have increased the limit enough so that it no longer matters.  Flash is also used in some synths for  REF _Ref42935246 \h Operating System storage; doing so makes it easier for the owner to install OS revisions.  
Foot Controller

Formant
A fixed-frequency  REF _Ref39425405 \h Notch Filter or set of notch filters.  Formants are responsible for the particular tone character of many sounds in nature; in particular, the strong set of formants created by the human mouth and vocal tract is what creates the distinct sounds of the human voice.  Specialized formant filter banks are designed to emulate this by providing a set of very narrow-band notch filters which can be set up in a desired relationship.  Since the formants do not track with the pitch of the sound being processed, they result in a tonal character that varies with the pitch.  The presence of strong formants presents a problem for  REF _Ref39563129 \h Pitch Shifters, which cannot easily hold the formants fixed while changing the pitch, but the newest generation of pitch shifters has at least partially overcome this problem  See also  REF _Ref43020993 \h Munchkinization.
Fourier Transform
A mathematical operation that breaks up a complex waveform into the component sine waves that make up that waveform.  As mathematicians say, the operation converts the waveform from the “time domain” (which corresponds to the picture that one would see if the waveform is fed into an oscilloscope) to the “frequency domain” (which corresponds to the display of the waveform on a  REF _Ref36032364 \h Spectrum Analyzer).  
Frame

FreeMIDI
A software package and interface standard developed by MOTU for tying  REF _Ref38201901 \h Sequencer software to MOTU’s line of  REF _Ref35841199 \h MIDI interface hardware.  Like OMS, the FreeMIDI system allows the user to build a description of what type of MIDI interface hardware is being used and which synths and other devices are using which  REF _Ref38206176 \h Channels.  FreeMIDI then provides this information to the sequencer software, and the sequencer can address the MIDI-devices without regard to what type of interface hardware is being used. Unlike most such MIDI interface libraries, MOTU has developed version for both the Windows and Mac platforms (not OSX, though).  MOTU has tried to promote FreeMIDI as an open standard, but it has never caught on with other hardware manufacturers.  
Frequency
The objective measurement of the cycle rate of an alternating signal, as opposed to the  REF _Ref39587552 \h Pitch.  (There is a tendency to use the two terms interchangeably; musicians are more likely to use “pitch” to refer to frequency, while engineers are more likely to do the opposite.)
Frequency Counter
A laboratory test instrument that displays numerically the fundamental (hopefully) frequency of an input signal.  Sometimes used for precision tuning of synths or other instruments, although the limitations of typical lab frequency counters must be understood.  (Most units are designed for testing digital circuits or radio transmission equipment, and they may produce false readings when presented with complex musical signals.)
Frequency Modulation
A variation in the frequency of a carrier signal, according to the instantaneous value of a modulating waveform.  When the modulation is of subsonic frequency, the result is a slow or rapid variation in the pitch of the carrier signal which is referred to as  REF _Ref41462883 \h Vibrato.  (Performers often use vibrato to make a sustained sound more interesting to the ear; this is a practice that long precedes the advent of synthesizers.  When used judiciously the effect is engaging, but over-use can make it cloying to the ear.)  When the modulation is of audio frequency, the result is a composite waveform containing a complex frequency spectrum mathematically related to the frequencies of the partials of the carrier and the modulation.  As it happens, frequency modulation is capable of mimicking the harmonic content of a wide variety of acoustic instruments, ranging from piano to trumpet to sitar.  The Yamaha DX7 synth of the 1980s exploited this characteristic, and many performers who originally bought this synth used it almost solely as a replacement for older Rhodes and Hohner electric pianos.  FM has a reputation for being a difficult method of synthesis to program sounds in; it is not always easy to know how to approach getting a particular type of sound or predict in advance the results of a particular patch.  Compare with  REF _Ref36142416 \h Amplitude Modulation.
Full Range Oscillator
An  REF _Ref38088628 \h Oscillator circuit capable of producing signals across the entire range of frequencies generally used in a synth, from  REF _Ref43562292 \h LFO frequencies (1 cycle / 10 seconds up to about 30 Hz) through most of the usable audio range (top end between 4 KHz and 15 KHz), all without any mode changes or switch throws.  Such designs are rare, particularly in  REF _Ref43562508 \h Analog oscillators; this 15+ octave range is among the widest range for any oscillator circuits found in any branch of electronics.  Due to this, old modular designs for full-range oscillators are highly prized among certain performers.  
Fundamental
The lowest-frequency sine wave in a  REF _Ref48314863 \h Harmonic Series; all other harmonics are multiples of the fundamental.  With most musical instruments, the frequency of the fundamental is what determines the  REF _Ref39587552 \h Pitch of the note played.  (Among the instruments which produce a definite pitch when played, the major exceptions to this rule are the bells and chimes; the mix of non-harmonic overtones these instruments produce usually results in a perceived pitch that is lower than the fundamental.)  
General MIDI
(Often abbreviated “GM”) An extension of the  REF _Ref35841199 \h MIDI standard which calls for a synth to have a standard set of sounds in each of its patch memory locations.  For instance, patch 1 might be a trumpet… [need realistic examples].  The idea behind General MIDI is that a composer can write a song that uses the General MIDI sounds and then send the song as a Standard MIDI File to an audience, and if the audience members have GM-compatible synths then they can load the MIDI file into their sequencers and play it, and it will sound the same as it did when played on the composer’s synth.  (Originally, the creators of General MIDI had in mind that home stereo systems might be equipped with GM-compliant synth circuits and that popular songs would be released in this format, somewhat like in the days of player pianos.  However, nearly all popular music today is vocal music, and GM lacks a way to reproduce vocals, so this particular use has never come to pass.)  General MIDI has acquired something of a bad reputation among musicians, mainly because of computer sound cards with poor-quality GM  sounds, coupled with Web pages which download obviously amateur MIDI sequences at unsuspecting users.  However, many of the workstation synths currently on the market have a bank of patch memory which contains good-quality GM-compliant patches, and there are also rackmount synths made specifically for reproducing General MIDI.  
General Purpose Controller
A category of   REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller messages which is defined in the standard as being left open for manufacturers to implement for whatever purposes they wish.  The standard defines four general-purpose controller numbers in the continuous-controller range, and four additional numbers in the on/off switch range.  
Guitar Synthesizer
A synth that uses a guitar, rather than a keyboard, as its controlling interface.  Guitar controllers can be divided into two categories, those that use a conventional guitar with  REF _Ref48315617 \h Pitch Converters detecting the notes played, and those that directly detect the hand motions of the player with touch pads and sensors.  (The latter type generally produce no sound of their own, and often bear little resemblance to a conventional guitar.)  Guitar synthesizers have always proven difficult to design and have often disappointed both their makers and their users.  (Development costs of the Avatar, one of the first guitar synths, are reputed to be what put the ARP synthesizer company out of business.)  As a result, after an initial burst of enthusiasm in the late ‘70s, they have never been highly popular.  However, Roland has kept at least one model in production throughout, and recently Parker and other guitar makers have been marketing a “MIDI guitar” ⎯ a guitar with a pitch converter built-in and a MIDI jack right on the guitar body, so that it can control a conventional synth without a separate converter box.  Other string instruments have also been interfaced to synths, notably the violins and other bowed string instruments marketed by Zeta and Barcus-Berry.  
Hammond Organ
An electronic organ, designed in the 1930s, that uses a unique sound synthesis method.  The Hammond organ can be thought of as a primitive  REF _Ref38091064 \h Additive Synthesis machine.  Sounds are made of a mix of a fundamental frequency plus harmonics up to the 9^th harmonic, and the first and second sub-harmonics. On most Hammonds sounds can be created with a set of “drawbars”, which are simply slider-type controls that are mounted so that they pull out or push into a panel, rather than sliding back and forth across the panel like conventional slider knobs.  Each drawbar controls the level of one individual tone.  To produce the tones, classic Hammond models use a “tonewheel” system.  A tonewheel is a metal plate, cut into the shape of a polyhedron or a mechanical gear, and rotating on a shaft.  A magnetic pickup is mounted near the edge of the rotating plate, and the plate induces a signal in the pickup as the bumps and variations of the plate pass by.  A typical model has about 90 wheels from which all of the tones for any given note can be formed.  (However, the lowest and highest notes don’t always have all of their tones; sometimes a tone an octave lower or higher is used for some of the harmonics of the extreme notes.  This is known as “foldback”.)  The wheels are all mounted on a common shaft which is driven by a rather peculiar motor arrangement; most have to be “started” in a manner rather like starting a car engine.  The keyboard is wired to a complex matrix of switches that selects the proper wheels for each key.  Hammonds have a classic sound commonly used in jazz and progressive rock, but the electromechanical models are not used as much as they were at one time due to their bulk, weight (most weigh over 300 lbs.), and need for maintenance.  However, the design was groundbreaking in the pre-WWII era, and it predated the emergence of “true”  REF _Ref48315743 \h Additive Synthesis by decades.  See also Rotating Speaker.  
Hard Disk Recording
The process of recording audio signals by digitizing the signals and writing the signal data to a computer’s disk drive, as opposed to using magnetic tape (which had been the standard in the post-World War II era up until recently).  Among other benefits, hard disk recording allows instant queing to any point, editing of individual tracks, and undoable editing ⎯ all things which were difficult or impossible with tape.
Harmonic
An individual sine wave in a  REF _Ref48314863 \h Harmonic Series.  
Harmonic Series
Part of the theory behind the  REF _Ref35840291 \h Fourier Transform holds that all waveforms are made up of a mix of sine waves of various frequencies.  For most musical instruments and many natural sounds, the frequencies of these sine waves obey the harmonic series.  A harmonic series considers of a sine wave at a particular frequency (referred to as the  REF _Ref48315934 \h Fundamental), and a series of higher tones which are referred to as harmonics.  Each harmonic is an integer multiple of the frequency of the fundamental; the second harmonic is twice the fundamental’s frequency, the third harmonic is 3x the fundamental, and so on.  Usually, the frequency of the fundamental determines the  REF _Ref39587552 \h Pitch of the note that the listener perceives, and the harmonics determine the timbre and character of the note.  (When a guitarist plays a “harmonic” at the 12^th fret, the guitarist is effectively demonstrating this theory; the finger touched lightly to the string effectively mutes the fundamental and some of the odd-numbered harmonics, changing the character of the normal string sound.)  Understanding of the harmonic series, and its effect on the ear, is essential to determining why a particular sound has the tonal characteristics that it has.  Some well-known waveform types can be precisely described mathematically in terms of harmonic series; for example, a square wave is made up of a fundamental and all odd-multiple harmonics mixed in a certain proportion.  
Hex Pickup
A guitar pickup which has an individual coil and output for each string.  Hex pickups (and they seem to be called this regardless of how many pickups or how many strings the unit actually has) are used most commonly as inputs to  REF _Ref48316455 \h Guitar Synthesizers, which have circuits for each string that detect the  REF _Ref46131352 \h Frequency and amplitude of the notes being played on each string.  These convert the information into control signals of some sort to control the synth proper.  Doing it this way is much easier, from a computational standpoint, then taking a single audio output from a guitar and trying to pick out the individual notes from a chord.  Some units also have an effect called “hex fuzz”, where each output from the pickup is run through an individual distortion circuit and the outputs of those are then combined.  Doing it this way prevents  REF _Ref46131848 \h Intermodulation from occurring within the distortion circuit, and so produces a different sound than a regular guitar fuzz box.
High Pass Filter
A filter that filters out frequencies below the  REF _Ref36446246 \h Cutoff Frequency.  High pass filters are used in synths to make sounds “brighter” or “tinny”.  High pass filters when set to extremes filter out the fundemental and lower harmonics that contribute to the sense of a sound’s pitch, leaving a cluster of high harmonics that may sound noisy or vague in pitch.
Hold 2

Inharmonic
A set of two or more signals or overtones which are not harmonically related, mathematically speaking.  See  REF _Ref39506288 \h Harmonic.
Intermodulation
An interaction between a pair of mixed signals within a circuit, such that the output contains additional frequencies, in some amount, that are the sum and difference of the frequencies of the signals in the input.  Intermodulation results from non-linearities in the circuit and is usually undesirable, although some devices (notably guitar distortion boxes) produce intermodulation as an intended result.  (The guitar “power chord”, consisting of the root and perfect fifth, when played into a distortion box intermodulates in such a way so as to add a minor third to the output; this is a fundamental characteristic of heavy metal and other forms of rock music that rely on heavily distorted guitar.)  See also  REF _Ref36143630 \h Ring Modulation.
Inversion

Lag Processor
A circuit which limits the rate at which a signal can increase or decrease in value (in amplifier terminology, this is known as “slew rate limiting”).  This circuit, or a software simulation of it, is most often used to produce  REF _Ref39587977 \h Portamento by processing the pitch control signal from a keyboard.
Laser Harp
A keyboard alternative that works by means of the performer passing the hand or fingers through beams of light to trigger notes and generate control signals.  (Most such devices don’t actually use lasers, due to the danger posed by accidental reflections, just focused beams of ordinary light.)  One notable performer who has used the laser harp extensively is Jean-Michel Jarre.
Layering
Playing two or more different patches or sounds with the same notes.  Layering can be accomplished with MIDI by having one synth be a slave unit to another synth, such that they both play the same notes; setting up different  REF _Ref38090765 \h Patches on the different units can produce sounds that, surprisingly, do not sound like merely a mix of the individual patches but something qualitatively different (depending on the patches used).  Today, it is more common to find  REF _Ref39408157 \h Multitimbral synths that can layer two or more  REF _Ref39590529 \h Voices, each sounding different patches, for each key pressed.  (The tradeoff is that the synth uses more voices this way, reducing the number of notes that can be played simultaneously.)  Layering can also be accomplished with a  REF _Ref38201901 \h Sequencer by copying one track’s notes and pasting them into another track at the same position in time.  
Local Control
A  REF _Ref35841199 \h MIDI message type that controls the ability of a synth to be played by means of its own keyboard.  The Local Control message has a parameter which may be “off” (zero) or “on” (nonzero).  When a synth with a keyboard receives a Local Control Off message, the sound-producing part of the synth and the keyboard act as two separate units; pressing a key will not produce a sound but will send messages out of the MIDI out port, while the sound-producing part of the synth will produce sound only in response to messages coming in through the MIDI in port.  Receiving a Local Control On message restores normal operation.  The Local Control capability facilitates use of the synth’s keyboard as a  REF _Ref38203151 \h Master Keyboard for controlling other synths (particularly  REF _Ref40073537 \h Rackmount Synthesizers which lack keyboards of their own); it prevents the synth from sounding when being used to control another synth (without the necessity of selecting a “silence”  REF _Ref38090765 \h Patch).  This is particularly useful for recording with a  REF _Ref38201901 \h Sequencer; generally in this type of setup Local Control is off and the user selects the synth to be played using the sequencer’s  REF _Ref40074547 \h Soft Thru capability.  (This could in fact be the synth with the keyboard, but with Local Control off, the notes have to go through the sequencer and back.)  
LFO
See  REF _Ref38202567 \h Low Frequency Oscillator.  
Loop

Low Frequency Oscillator
An oscillator designed to produce signals whose frequency is at the bottom of, or below, the audio range.  Nearly all synths have at least one LFO or a digital equivalent.  It is useful for producing a repeating control signal for a wide variety of purposes; when added to the control input of a VCO it produces the effect known as vibrato, and if it is added to the control signal of a VCA, it produces tremolo.  A typical LFO can generate a variety of useful waveforms, including sine, triangle, square, ramp-up, and ramp-down.  The most useful LFOs have an upper frequency limit above 100 Hz and a lower limit below 1 Hz (such frequencies may be given as seconds/cycle; for instance, a frequency of 20 seconds/cycle corresponds to 0.05 Hz).  
Low Pass Filter
A filter that filters out frequencies above the  REF _Ref36446246 \h Cutoff Frequency.  Low-pass filters are used in synths to attenuate high harmonics and make sounds “darker” or “smoother” in timbre.  Low pass filters are used frequently as signal modifiers in synths in part because of the way the harmonic series works; the low pass filter leaves the fundamental of the signal intact, and so it doesn’t (usually) effect the subjective pitch of the signal.  See also high pass filter.  
Martenot

MAS

MAX/MSP
A programming language for writing digital synthesis and signal processing algorithms on general-purpose computers.  It is similar in intent to  REF _Ref72915364 \h Csound, although very different in design.  Unlike Csound, The MAX/MSP language interpreter is a commercial product, originally designed by the now-defunct Opcode company but now supported by Cycling ’74.  
Master Keyboard
A keyboard used to play a number of separate synthesizers through  REF _Ref35841199 \h MIDI messages.  A master keyboard may be a conventional synth, electronic piano, etc., but it may also be a  REF _Ref36141523 \h Controller keyboard with no sound generation circuitry of its own.  
Mellotron
An early form of sample playback synth, commonly used in the 1960s and ‘70s.  The Mellotron produced sounds by means of strips of magnetic tape containing pre-recorded instrument sounds.  Each key had its own strip of tape, which normally lay motionless atop a continuously rotating smooth capstan.  Pressing the key pressed a pinch roller against the capstan, pulling the tape through and across a playback head.  When the key was released, a spring mechanism pulled the tape back to the beginning; doing this ensured that playback always started at the same point of the tape in order to realistically reproduce the attack transients and articulation of the recorded instrument sound.  A capstan motor speed control provided some tuning and pitch bend capability; other than that and an overall tone control, no means of modifying the played-back sound was provided.  The Mellotron was particularly noted for its string and flute sounds, and was prominent in 1970s progressive rock.  However, it was notorious for mechanical complexity and frequent need of maintenance.  The company that manufactured them is now out of business and the relatively few remaining units are nearly all in the hands of collectors.  The Mellotron sound remains popular in certain forms of music and recently some manufacturers have offered sampled sound banks of sounds taken from the Mellotron (samples of samples!).
Merge
(1) A  REF _Ref35841199 \h MIDI interface device which combines two or more streams of data from different senders into one data stream, and the function that such a device performs.  (2) A  REF _Ref38201901 \h Sequencer function which combines the MIDI data recorded in two or more tracks into one track.
MIDI
An acronym for “Musical Instrument Digital Interface”.  This is a communications system and set of software protocols allowing synthesizers and sequencers to control other units via remote control.  The physical interface takes the form of cables with a 5-pin male DIN plug at each end.  The communications protocol uses sequences of 8-bit bytes, transmitted via an asynchronous start/stop serial method similar to the common RS-232 serial standard.  Each message begins with one byte that specifies a message type and (in most cases) a channel number, optionally followed by one or more bytes that contain parameter values for the message.  
MIDI Clock
A  REF _Ref35841199 \h MIDI message that is sent out by a timing source in order to mark the passage of time to the receiving unit or units.  The MIDI Clock message was defined in the original 1980s MIDI standard as a primitive method of achieving  REF _Ref43562914 \h Synchronization between  REF _Ref38201901 \h Sequencers and  REF _Ref43562957 \h Drum Machines, tape units, etc.; it predates the  REF _Ref43563007 \h MIDI Time Code.  The unit providing the time reference sends out a MIDI Clock message every ??? clocks.  A MIDI Clock message is only a “tick” that marks the passage of time.  It does not actually tell the time, which means that it can maintain units in synchronization but cannot automatically put units in sync unless they are synchronized by other means prior to starting up.  Due to this limitation, MIDI Clock has been replaced by MIDI Time Code for most purposes.
MIDI Machine Control

MIDI Manager
An old standard for MIDI interface drivers once used on Apple computers.  At the time it was developed (around 1990), Apple was making an effort to standardize all types of hardware interfaces in the MacOS operating system; MIDI Manager was the first such standard of its kind.  However, it was rapidly surpassed in features by Opcode’s  REF _Ref39934817 \h OMS and MOTU’s  REF _Ref39934833 \h FreeMIDI.  Apple soon abandoned further development of MIDI Manager due to legal complications, and most developers and users had migrated away from it by 1995.
MIDI Time Code
(Acronym MTC) As the name suggests, this is a time code that is transmitted via MIDI, and a considerable improvement over the older  REF _Ref43563586 \h MIDI Clock message standard.  Basically MTC is a re-coding of the  REF _Ref43013674 \h SMPTE time code standard such that SMPTE times can be transmitted via MIDI; the way it measures time is similar enough that a converter box can easily convert an incoming SMPTE time code signal into MTC or vice versa.  In MTC, the time source transmits four  REF _Ref43563626 \h Quarter Frame per SMPTE frame.  The Quarter Frame messages themselves mark time, but also each one carries a part of the current SMPTE hour:minute:second:frame time value.  After enough Quarter Frame messages have been received, the receiver can assemble the received data and discover the current absolute SMPTE time; by this method devices can achieve  REF _Ref43562914 \h Synchronization from a “cold start” without any prior cueing.  
mLAN

Modular Synthesizer
A synth which is constructed from discrete functional blocks, which the user can purchase and install individually as needed to construct any desired configuration.  The first practical synthesizers as we know them today, beginning with the work of Donald Buchla and Bob Moog in the early 1960s, were modular in construction.  In a typical modular synth, all signals within each module are accessible externally and are routed by the use of  REF _Ref38089200 \h Patch Cords.  Because of this, modular synths are considered by many to be the ultimate in complex-sound creativity, as the number of possible signal routings in any non-trivial configuration is nearly infinite, and the system is fully open to interconnection with external devices at any point in the signal chain.  However, this flexibility and lack of pre-wired connections makes this type of synth difficult to learn and to play.  Also, the modular method of construction is relatively space- and cost-inefficient, meaning that a large configuration will require a substantial amount of time, space, and money to set up.  (Among other things, this means that as a practical matter most modular synths are monophonic, as a polyphonic setup requires multiple copies of everything.)  All current modular synths employ analog signal routing and most of the module circuitry is analog, although there are some digital processing modules available.  Modular synths disappeared from the market in the 1980s, but since about 1997 have made a significant comeback, with over a dozen manufacturers currently active in the market.  
Modulation
(1) In general, periodic variation of a waveform, in which some aspect of the waveform is varied usually according to the instantaneous value of some other waveform.  The waveform being varied is often called the “carrier”, while the waveform that controls the modulation is itself often called the “modulation”.  Many mathematically specified types of modulation exist, such as amplitude modulation and frequency modulation.  (2)  REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller message type number 1, which conventionally instructs the receiver to apply an LFO to the frequency of the generated waveform in order to produce vibrato.  
Mod Wheel
An auxiliary performance control on a keyboard which varies the  REF _Ref36141657 \h Modulation of the waveform (or generates the  REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller Modulation message to tell the receiving synth to do so).  On many keyboards the mod wheel is a large thumbwheel identical to, and alongside, the  REF _Ref36141700 \h Pitch Wheel.  On others it may be combined with the pitch wheel function, usually in the form of a joystick.  A notable implementation is the Roland T-shaped pitch wheel, which produces modulation when the wheel is pushed sideways away from the player.  
Monophonic
(1) A synth capable of playing only one note at a time; the opposite of  REF _Ref38124932 \h Polyphonic. (2) A mode in which the synth plays only one note at a time; the note might apply to only part of a Split keyboard.  See also  REF _Ref39590423 \h Unison.
Monotimbral
A synth capable of playing only one patch, or timbre, at a time; the opposite of  REF _Ref39408157 \h Multitimbral.
Multitimbral
A synth capable of playing more than one patch, or timbre, at a time.  Until fairly recently (about 1990), this was a feature found only on high-end synths, but with processing and memory capacity getting less expensive, it is now appearing on more affordable systems (although it is still by no means universal).  Due to the fact that many of today’s synths use DSP processors for sound generation and effects, and because DSPs can be reassigned to different functions, some multitimbral synths have two operating modes ⎯ the multitimbral mode, and a  REF _Ref39408195 \h Monotimbral mode in which the tradeoff is the availability of more voices or additional effects.  On a traditional multitimbral instrument such as a pipe organ, the control of the different timbres is provided for by having a multi-manual keyboard, but since very few synths are built with multiple manuals, this control is usually provided either by employing a keyboard split, or by assigning each timbre to external control via a separate MIDI  REF _Ref38206176 \h Channel.
Munchkinization
An effect occurring when a sound with strong  REF _Ref43021014 \h Formant characteristics is shifted severely in pitch using a  REF _Ref39563129 \h Pitch Shifter, resulting in a noticeably peculiar timbre.  The name comes from the canonical example of shifting the human voice upwards, resulting in an effect often compared to the Munchkin voices from the movie “The Wizard of Oz”.  
Noise
Generally, a signal containing such a broad frequency spectrum that it is impossible to discern a particular pitch.  Noise usually produces a hissing, crackling, or rumbling sound depending on how it is filtered.  The two most common noise circuits usually found in synths are  REF _Ref36144288 \h White Noise and  REF _Ref36144297 \h Pink Noise.
Noodle
A  REF _Ref54081240 \h Self-Running Patch.
Normalled
A “behind-the-panel” connection which exists in a  REF _Ref38088112 \h Patch Bay or panel.  A normalled connection provides a default signal routing between an output and an input which is made automatically when no  REF _Ref38089200 \h Patch Cord is plugged into the either the input or the output.  A “half-normalled” connection is interrupted only when a cord is plugged into the input; plugging a cord into the output creates a “Y” output to both the patch cord and the normalled input.  (Usage on this is sometimes sloppy; “normalled” is often used to refer to either type.)
Normalization
The process of scaling the level of a digitally stored signal so that it produces the maximum possible output level without clipping or aliasing.  This is a common feature in  REF _Ref36140518 \h Samplers and digital recording systems to maximize the signal-to-noise performance on playback.
Notch Filter
A  REF _Ref36446120 \h Filter that eliminates frequencies in a band around a center frequency, leaving frequencies both above and below the band intact.  It can be thought of as the functional opposite of a  REF _Ref72920870 \h Bandpass Filter, and in fact it is sometimes implemented by inverting the output of a bandpass filter and combining that with the original signal.
Note Off
A  REF _Ref35841199 \h MIDI message that tells the receiver to stop sounding a note, or more specifically, to transition the note to the release phase of its envelope.  (If the release time is long, it may be some time before the note actually stops sounding.)  The message contains the note number of the note to release, and an extra byte which may contain a  REF _Ref43021173 \h Release Velocity value.
Note On
A  REF _Ref35841199 \h MIDI message that tells the receiver to begin sounding a note.  The message contains the note number of the note, and a  REF _Ref36034039 \h Velocity value that encodes how rapidly or with how much force the key was pressed.  The receiver is supposed to use the velocity value to scale the amplitude and/or attack time of the note sounded; it may also use the value to perform other functions, such velocity switching on a sampler.  
NRPN

Omni Mode
A mode in which a  REF _Ref35841199 \h MIDI receiver receives and acts on any data that arrives on any  REF _Ref38206176 \h Channel.
OMS
A software package, used on the Mac platform, for tying  REF _Ref38201901 \h Sequencer software to  REF _Ref35841199 \h MIDI interface hardware.  (OMS originally stood for Opcode Music System, after the Opcode company which wrote it.  Later, they changed the acronym to Open Music System after Opcode opened the specification up to third-party developers.)  The OMS system allows the user to build a description of what type of MIDI interface hardware is being used and which synths and other devices are using which  REF _Ref38206176 \h Channels.  OMS then provides this information to the sequencer software, and the sequencer can address the MIDI-using devices without regard to what type of interface hardware is being used.  OMS has been at the center of a long and strange odyssey for Mac developers and users.  The software has been unsupported since 2000 when Gibson purchased and effectively disbanded Opcode, but it remained in use because legal restrictions prevented Apple from developing a replacement.  These problems were finally solved, and the OSX operating system has introduced a new MIDI system; with this OMS is expected to finally fade away.
Operator
(1) A mathematical or physical entity that performs some combining or transforming function on a signal or set of signals.  (2) Term popularized by Yamaha to refer to an  REF _Ref38088628 \h Oscillator in a synth that employs  REF _Ref36143656 \h Frequency Modulation synthesis.  
Operating System
(1) On a computer, the software which allows the system to boot up, presents the basic user interface (command line or windowing-type interface), and provides a foundation of essential system services for application software to use.  (2) When referring to synths and other dedicated-type devices (as opposed to general-purpose desktop computers), there is a tendency to refer to all software that runs on the unit as the “operating  system”.  This is not strictly correct in computer-science terms, but since vendors of such hardware almost never sell or provide application software for this hardware independently, from the user’s point of view there is no difference.
Oscillator
(1) A circuit that produces a repeating waveform.  Oscillators in synths are used as either sources of audio signals, or as sources of control signals used to produce cyclical changes in other circuits.  (2) A software component that produces a waveform.  In this context, the term is often used to refer to components producing waveforms that are not strictly repetitive, such as sample playback routines.
Pad

Pan
(1) In general, to position or move the apparent location of a sound source within a stereo (or surround sound) field.  (2) In relation to electronic music in particular, a function of a synth that controls the relative level of a specific signal in the left and right outputs of a synth having stereo outputs; some synths having stereo VCAs allow for panning to be controlled by a control signal (see Ping-Pong).  (3) A  REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller message, using controller type 10, which causes the receiver to execute a pan function.  
Panic Button
A feature of some  REF _Ref38203151 \h Master Keyboards, MIDI interface devices and auxiliary MIDI processing boxes.  This consists of a physical button on the box that, when pressed, sends an  REF _Ref38091154 \h All Notes Off message on all  REF _Ref38206176 \h Channels to all connected MIDI devices.  Panic buttons are also provided by sequencer software as a clickable button in a window, or a key or combination of keys on the computer’s alpha keyboard to press (such as the ESC key, or the Command-period combination familiar to Mac users).  
Passive
An electronics component or circuit that does not need a power supply in order to operate.  
Patch
(1) A configuration of signal routings accomplished by plugging patch cables into locations in a patch bay, linking a chain of inputs and outputs so that the signal gets sent where it needs to go.  (2) On a synthesizer, a set of parameters settings and signal routings that produces a particular sound.  Originally this meaning was very close to the first meaning, in that on the original modular synthesizers, sounds were formed by using patch cords to route signals from one module to another.  (The classic  REF _Ref39408891 \h Modular Synthesizer had no built-in signal routing and produced no sound until a patch was set up.)  With the advent of synths with patch memory, this meaning got extended to refer to both the internal signal routing and switching, but also all of the settable parameters in the synth’s signal processing circuits.
Patch Bay
(Also referred to as “patch panel”) A panel, generally mounted in a rack, containing (usually) two rows of jacks which are wired to inputs and outputs of various signal generating, processing, and/or reproducing devices.  By convention, outputs appear in the top row, with inputs in the bottom row; the placement of an output above an input in the patch bay’s layout may imply the presence of a  REF _Ref38090148 \h Normalled connection between the output and the input.  Connections are made by plugging patch cords into the output and input jacks to send signals from outputs to inputs as needed.
Patch Cord
An interconnection cord that is intended to make a connection between an input and an output of a  REF _Ref38088112 \h Patch Bay or panel.  Typically these cords are shorter (1 to 3 feet in length) and somewhat less sturdily constructed than cords used to, for instance, connect instruments to a mixer.  
Patch Editor
A computer program that allows  REF _Ref38090765 \h Patch data to be loaded in from a synth, edited graphically on the computer’s screen, and the edits sent back to the synth.  A patch editor can be a big help when editing patches on a synth equipped with a clumsy menu interface.  There have been synths (such as the Alesis Nanosynth) which for reasons of economy in packaging have been designed with no built-in editing controls at all; patch editing is accomplished entirely with a patch editor program supplied with the synth.  
Patch Librarian
A computer program that stores and loads  REF _Ref38090765 \h Patch data from/to a synth.  A patch librarian is handy for organizing collections of patches, allowing patches to be categorized and usually stored with an “extended name” which is longer and more descriptive than the name that is displayed on the synth itself (if the synth even stores patch names at all).  It allows patches to be rearranged into different banks and groups with different patch number assignments, for supporting different working situations (such as sets at a gig), and it effectively extends the synth’s patch memory by allowing patches not being used at the moment to be stored on the computer’s hard disk instead of in the synth.  Some patch librarians also have the ability to .  Nearly all patch librarians today use  REF _Ref35841199 \h MIDI to interface with the synths they control.  
Patch Memory
Phaser
Piano Weighting
(1) A method of constructing a keyboard such that it duplicates the feel of the hammer action of a piano.  (2) More generally, any keyboard constructed with heavily weighted and damped keys, designed to feel familiar to players trained on piano.  Compare with  REF _Ref39932205 \h Synth Weighting.
Pin Matrix
An alternative to using  REF _Ref38089200 \h Patch Cords to establish signal routing in certain  REF _Ref41464606 \h Semi-Modular and  REF _Ref39408891 \h Modular Synthesizer models.  In a pin matrix, all signals are brought to a set of horizontal and vertical bars mounted behind a grid of holes.  Signal outputs are connected to the horizontal bars and inputs are connected to the vertical bars (or vice versa).  Inserting a metal pin in a hole establishes a contact between a horizontal bar and a vertical bar, hence establishing a routing.  Synths that have used a pin matrix include the EMS Synthi-A and the ARP 2500.  The pin matrix makes for a much more tidy front panel than the traditional arrangement of patch jacks and cords (which tends to result in patch cords hanging in front of the knobs that one is trying to reach), but this design is also more expensive, takes up more room, and can cause signal quality problems (the ARP 2500 was notorious for signal crosstalk originating in the pin matrix).  
Ping-Pong
Rapidly panning or switching a sound between the left and right channels in a stereo mix.  Some synths, under control voltage or MIDI control, are capable of panning a sound across the mix much faster than a human hand operating a mixer pan control could do so, producing a unique disorienting effect on the listener (particular when listening through headphones).  Judicious use of the technique can be quite dramatic, but it was overused in the early days electronic music and to many listeners the effect is clichéd.  
Pink Noise
Noise which has been filtered so that it has equal energy at every frequency.  If pink noise is analyzed in the frequency domain, using a logarithmic scale with constant interval per octave, the result is a flat line.  Because of this, pink noise sounds somewhat less hissy than  REF _Ref36144288 \h White Noise.
Pitch
The perceived fundemental frequency of a sound (as opposed to the objective measurement of frequency as measured by a frequency counter or oscilloscope).  Several psychoacoustic phenomena exist which can cause the pitch, as perceived by the human ear, to differ from the actual frequency.  This is often true for three-dimensional percussion instruments such as bells and chimes, and this makes the sounds of these instruments particularly difficult to imitate with conventional synthesis techniques.  (See the entry for  REF _Ref36143630 \h Ring Modulation for more info.)
Pitch Converter
An electronic circuit that analyzes the pitch of an input signal, and produces a control signal that represents the pitch.  The first pitch converters made in the 1970s usually output a control voltage, for control of the  REF _Ref39424455 \h Analog Synthesizers of the day, but devices made today nearly always output a MIDI signal.  Pitch converters allow conventional instruments and human voices to be used to control synthesizers, as an alternative to a keyboard.  
Pitch Shifter
A device which raises or lowers the frequency of an input signal, in real time.  The pitch shifter accomplishes this bit of sonic prestidigitation by digitally chopping the signal up into small chunks and then playing back the chunks faster or slower than the input rate.  To make up the time difference, the pitch shifter must introduce splices into the signal; one of the distinguishing characteristics of a good unit is how well it covers up these splice points in the output.  Pitch shifters are sometimes known as “Harmonizers”, but that word is a trademark of Eventide, which introduced the first practical pitch shifter in 1976,
Pitch Wheel
(1) A control on a synthesizer which raises or lowers the pitch of the notes being sounded.  On most modern synths, the pitch range of the wheel can be programmed as part of the patch; older units usually have a fixed range of ± one octave.  This is intended as a performance control, as opposed to a tuning mechanism.  Most synthesizers implement this as a rather large thumbwheel control, mounted such that the direction of motion is front-to-back, and spring loaded so that it returns to the neutral position when released.  (2) A  REF _Ref35841199 \h MIDI message type which conventionally is sent by the transmitting unit when the pitch wheel is moved, and is interpreted by the receiving unit as a request to alter the pitch.  
Plug-In
In general, a unit of computer code that can be added to a program to extend the program’s functionality.  However, in the electronic music world, the term usually refers specifically to code units that can be added to a software-based  REF _Ref38201901 \h Sequencer to add effects and perform other modifications to recorded audio signals.  A number of standards for specifying how the plug-ins are to interface with the sequencer software exist, and when buying plug-ins it is important to be aware of which standards one’s sequencing software supports.  Commonly used standards are: [list].  More recently, some vendors of  REF _Ref39587487 \h Soft Synths have begun implementing them as plug-ins, which usually provides better integration and more features than having the soft synth run as a stand-alone program.
Polyphonic
Refers to an instrument which is capable of sounding more than one note at a time; the term is usually used in the context of synths and other keyboard-based instruments.  A keyboard instrument said to be “fully polyphonic” is capable of simultaneously sounding a note for every key on the keyboard, such as an organ or piano; synthesizers with this property are rare.  Up until the mid-1970s, nearly all synths were monophonic, capable of sounding only one note at a time; to play chords one had to resort to tedious multitrack recording ⎯ one track for each note in the chord.  In the 1970s, two approaches emerged for designing polyphonic synthesizers.  One school of thought used top-octave division; the other employed a set of voice circuits capable of producing a limited number of simultaneous notes (4-8 was typical for the early designs) and used a microprocessor to assign played notes to the voices.  The top-octave division approach was capable of full polyphony, but inherent problems with limited control over the generated waveforms were never solved, and so the voice set approach came to dominate the field.   
Polyphonic Aftertouch
An  REF _Ref38125013 \h Aftertouch implementation in which there is a separate signal for each key of the keyboard, corresponding to the force being applied to that key.  The  REF _Ref35841199 \h MIDI standard calls the message that transmits this information “key pressure”.  Unlike channel aftertouch, polyphonic aftertouch has to be transmitted over MIDI as a separate stream of messages for each key; consequently it is capable of generating large amounts of data.  Because of this, and because of the complexity of implementing it, few keyboards offer polyphonic aftertouch.  (However, many sequencers allow the user to edit in poly aftertouch message manually, and there are synths that can receive poly aftertouch over MIDI even though they can’t generate it.)  Compare with  REF _Ref38125428 \h Channel Aftertouch.  
Portamento

Portamento Time

Preset

Preset Synth
A synth which is programmed with a set of  REF _Ref38090765 \h Patches at the factory, with little or no capability for the user to edit or store changes to the factory patches.  Most electric organs and digital pianos can be regarded as present synths.  A range of preset synths were produced in the 1970s as a work-around to the problem that the technology of the time made the construction of  REF _Ref38124932 \h Polyphonic synths very expensive.  Manufacturers realized that by replicating certain basic circuit blocks, they could build a polyphonic synth capable of producing a small, limited set of sounds, and so they built units producing sounds which performers of the day most wanted in a polyphonic unit (mainly string and piano sounds).  These types of designs went by the wayside in the ‘80s when technology improvements made general-purpose polyphonic synths more affordable.  
Program Change
A  REF _Ref35841199 \h MIDI message that tells the receiver to change to another  REF _Ref38090765 \h Patch.  The message contains a number in the range of 0-127 telling the receiver which patch to select.  (On many synths, the unit’s panel display which shows the selected patch numbers the patches differently than the numbering convention that the Program Change message uses; the user must consult the manual to see how the program numbers are mapped to displayed patch numbers.)  Most synths with patch memory will send a Program Change message when a patch is selected.  See also  REF _Ref39471437 \h Bank Select.  
Programmer

Pulse Wave
A waveform that alternates between a maximum value and a minimum value, returning to a zero value in between the pulses.  The width of the pulses is commonly expressed as the percentage of time within each cycle that the waveform is at the maximum value; this is commonly called the “duty cycle”.  (By this definition, a 50% duty cycle is a  REF _Ref38380516 \h Square Wave.)  Narrow pulses have a nasal, reedy sound; wider pulses sound more mellow.  
Pulse Width Modulation
A capability of some  REF _Ref38380779 \h Pulse Wave  REF _Ref38088628 \h Oscillators to vary the pulse width (duty cycle) of the pulses according to the value of a control signal.  Continuously varying the pulse width simulates the effect of having two  REF _Ref38380516 \h Square Wave oscillators varying in phase with respect to each other (as if slightly out of tune); it creates a full, spacious sound.  
Quantization

Quarter Frame

Rackmount Synthesizer
Basically, a synthesizer lacking a keyboard or any other built-in means for playing it.  With today’s miniaturized electronics, it is possible to build a working synthesizer in a space much smaller than that required for a keyboard enclosure; by divorcing the synth electronics from the keyboard, the synth can be packaged in a much smaller form factor.  Typically, an enclosure designed to be mounted in a standard 19” equipment rack is chosen, hence the name.  Since the rackmount synth lacks a keyboard, it must be played by some external means; the problem is easily solved by a  REF _Ref35841199 \h MIDI interface allowing the synth to be played by another synth with a keyboard, a  REF _Ref38203151 \h Master Keyboard, or a  REF _Ref38201901 \h Sequencer.  Many synths today are sold in both keyboard and rackmount versions, and the rackmount nearly always costs several hundred dollars less, so the enterprising player who already has a good keyboard or other means of control can save money by buying additional synths as rackmounts.  One disadvantage of the rackmount synth is that there is relatively little panel space for control knobs or switches, meaning that  REF _Ref38090765 \h Patch editing and control operations have to be accomplished by either a user-unfriendly data slider interface, or via some means of external control.  
RAM
An acronym for Random-Access Memory, which is just a fancy way of saying that the memory in question can be read or written at will.  (As opposed to  REF _Ref72914985 \h ROM, which has restrictions on when and how many times it can be written to.)  Ordinary RAM is used in synths for performer-editable  REF _Ref73167052 \h Patch Memory, as well as  REF _Ref42935246 \h Operating System uses, and RAM usually accounts for nearly all of the memory available in modern personal computers.  Most types of RAM have the disadvantage that they are volatile; that is, they become erased if power is removed.  Since performers don’t want to lose their patch memory every time they turn their synths off,  synth manufacturers get around this problem by installing long-life, low-power batteries which maintain power to the memory when the synth is off.  Of course, these batteries have to be replaced eventually.  Some synths automatically back up patch memory to some form of non-volatile memory and then use it to restore the RAM at the next power up.
Ramp Wave

Release
(1) The final phase of the signal produced by an  REF _Ref42917501 \h Envelope Generator, in which the signal drops to a zero or “base” level from which the generator will start the next time it is triggered.  (2) The time between when a key is let up by the performer and when the note stops sounding.  See 
Release Velocity
A rather obscure feature of the  REF _Ref35841199 \h MIDI standard.  When a key is released, the keyboard can measure how fast the performer allows the key to spring back up, and insert the value into the resulting  REF _Ref36033058 \h Note Off message.  What the receiving entity is supposed to do with this information is not specified in the standard.  In practice, few synths or keyboards implement this.
Resampling
A feature of some  REF _Ref36140518 \h Samplers which allows the performer to assemble one or more  REF _Ref38090765 \h Patches and  REF _Ref36140582 \h Samples, possibly with  REF _Ref43564274 \h Layering and  REF _Ref43564365 \h Effects, and then play notes while the sampler simultaneously records new samples of the played notes.  In this manner a very complex built-up sound can be reduced to a single sample.  This frees up resources in the sampler (such as allowing a note to be played with a single  REF _Ref39590529 \h Voice instead of requiring multiple voices), and it allows the new complex sound to be combined with other sounds ⎯ possibly for further resampling.
Reset All Controllers
A  REF _Ref35841199 \h MIDI message that tells the receiver to assume that the  REF _Ref41442932 \h Sustain Pedal has been released, the  REF _Ref36141700 \h Pitch Wheel has been returned to its neutral position, and that the  REF _Ref41442976 \h Mod Wheel and other  REF _Ref36141523 \h Controllers have all been returned to their zero positions.  Most commonly, this message is sent by a  REF _Ref38201901 \h Sequencer so that, if playback is stopped in the middle of a passage containing a pitch bend, the bend isn’t left “dangling” in the receiving synth (which can be confusing to the player if he/she subsequently attempts to play the synth after stopping the sequencer).  
Resynthesis

Rectifier

Reverb
The effect of a sound dying away gradually, as if played inside a room with hard, reflective walls.  
Reverse Echo

Reverse Reverb

Ribbon Controller
An auxiliary performance controller, sometimes provided as an alternative to a  REF _Ref36141700 \h Pitch Wheel or other control device.  A ribbon controller consists of a conductive ribbon, generally about 1 inch (2.5 cm) wide and mounted left to right, with a smooth insulating top layer.  It produces a control signal which is proportional to where the ribbon is touched, and the smooth surface allows the player to slide a finger back and forth to produce continuous changes.  
Ring Modulation
A type of  REF _Ref36142416 \h Amplitude Modulation where the input levels of the carrier and modulation signals are balanced such that the original carrier and modulation frequencies disappear totally from the output, leaving only the sum and difference frequencies.  The resulting frequencies are almost guaranteed to not be harmonically related, and ring modulation is often used to simulate the sounds of tuned percussion instruments that produce non-harmonic frequency spectra, such as bells and chimes.  Ring modulation can be a very difficult effect to control.
ROM
An acronym for “Read-Only Memory”, which is memory that cannot be altered once its initial contents have been written.  (This may not always be strictly true; there are “Programmable Read-Only Memory” [PROM] devices which can be re-written, but such usually involves installing them in a special programming fixture.)  ROM memory is frequently used in synths for information which is not expected to change, such as the  REF _Ref42935246 \h Operating System and the  REF _Ref42935259 \h Factory Presets; it is so used because once written it does not require power to retain its contents and it is nearly invulnerable to electrostatic discharges and other adverse conditions that can upset the contents of  REF _Ref42935370 \h RAM memory.  However, recently some makers of more complicated devices have taken to using  REF _Ref42935442 \h Flash Memory for this type of data so that occasional updates can be released and installed by users in the field.  (Update of data in ROM is difficult for most users, since it involves physically removing the ROM circuits from the circuit board.)
Rompler
A derisive term for a  REF _Ref41466653 \h Sample Playback synth, stemming from the fact that such units often appear in stale pop music in which the performer uses the synth strictly as a cheap substitute for a piano, horn section, drummer, etc.  This is somewhat unfair as some sample playback units actually possess fairly powerful synthesis features (an example is the Proteus line from E-mu), but players who own such units sometimes don’t dig far enough into the manual to find out how to use them.
RPN
(Acronym for “Registered Parameter Number”) A method of extending the  REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller specification to add more, less-used parameter types.  This involves using two controller numbers; a RPN control message (controller #???) is first sent to specify which parameter is to be controlled, and then one or more  REF _Ref46129754 \h Data Entry messages is sent to control the value of that parameter.  The selected parameter remains in effect until another RPN controller message is sent.  The assignment of RPN numbers is controlled in the MIDI standard.  Although there are a large number of assigned parameters, the only commonly implemented ones are  REF _Ref46129911 \h Portamento Time (RPN #???) and Master Tune (RPN #???).  See also  REF _Ref46129938 \h NRPN.
RTAS

S-Trigger
A type of trigger signal used by older Moog synthesizers.  This type of control signal is rather peculiar in that it relies on the receiver of the signal to supply power to the signal line (through a pull-up resistor); the sender signals the trigger by shorting the signal line.  Because this type of signaling is so peculiar (compared to what is usually used in synths), the Moogs that used it used a unique connector for it, a two-bladed connector that somewhat resembles an old-fashioned ungrounded power connector.  
Sample
A short amount of a recorded sound, usually ranging from a fraction of a second to a few seconds, intended to capture the essence of the sound being sampled.  All modern  REF _Ref36140518 \h Sampler synths digitize the sampled sounds and use digital memory to store the samples.  
Sample and Hold
An electronic circuit that, when activated by a trigger signal, measures the instantaneous value (usually the voltage) of an input signal, and then generates an output signal corresponding to this instantaneous value.  The output signal value is then held constant (ignoring any further changes in the input signal) until the circuit is triggered again.  
Sample Playback
A synth that plays back pre-recorded  REF _Ref36140582 \h Samples, usually stored in ROM in the unit’s memory.  Sample playback synths are widely used for reproducing acoustic instruments (a particular specialty is that of reproducing piano sounds), and are generally used for electronic production of music that is not normally considered “electronic” music.  This category of synth has acquired somewhat of a poor reputation for discouraging creativity and for encouraging the production of “formula” music; it has also been criticized as a cheap and cheesy replacement for real musicians.  However, a unit with realistic sounds can enable the creation of music whose production would otherwise be impractical or unaffordable; for example, a classical music composer can write for orchestra instruments and hear the results immediately, instead of having to wait for a real orchestra to perform the work.   And a well-designed sample playback unit can offer considerable capability for modulating and modifying the sounds it contains (consider, for example, the well-thought-out E-mu line).  Sample playback units have no sample recording capability of their own, although some can be expanded by either adding sound cards or by importing sample files from other synths.  
Sampler
A synth which has the ability to record and digitize short lengths (samples) of arbitrary sounds, and uses these as its waveform source (as opposed to using oscillators or other waveform-generating circults).  A sampler has the ability to pitch-shift a recorded sound to correspond to the key played on the keyboard, allowing non-musical sounds such as spoken words, automobile engines, pots and pans, etc., to be played.  (The first sample ever recorded on the first sampler was a barking dog.)  The Fairlight CMI is known today as the first sampler, but it wasn’t really designed to do this; the first synth designed specifically as a sampler was the E-mu Emulator. 
Self-Oscillation
Said of a circuit (one not intended to be an  REF _Ref38088628 \h Oscillator) which begins producing an oscillating output at certain control settings.  In synthesizers, this term is nearly always used in the context of  REF _Ref36446120 \h Filters; many analog filter circuits will begin oscillating when the Resonance is turned up sufficiently high.  Some performers make use of this, and a certain way to start a flame war among synth players is to venture an opinion on whether this constitutes a bug or a feature.  (Enough players hold the latter opinion that software filtering algorithms, which do not inherently exhibit self-oscillation, sometimes have code added to them to intentionally produce it.)
Self-Running Patch
A  REF _Ref38090765 \h Patch (particularly one executed on a  REF _Ref39408891 \h Modular Synthesizer) which, once configured and set into operation, generates sound or a combination of sounds indefinitely, without further input from the performer.  Such patches are often executed on modular synths using either an analog type of  REF _Ref38201901 \h Sequencer, or a combination of  REF _Ref54081149 \h Control Voltage processors arranged in devious ways so as to produce continuously varying patterns.  Surprisingly, some such patches are so well designed that one can listen to them for literally hours without becoming fatigued.  
Semi-Modular
A synthesizer which resembles a  REF _Ref39408891 \h Modular Synthesizer, but with a typical collection of circuits and modules mounted in a single box.  A semi-modular is not easily alterable as a true modular is, but it still takes  REF _Ref38089200 \h Patch Cords for signal routing, providing the same flexibility in routing and combining with external circuitry as a true modular.  A feature of most semi-modulars is the addition of  REF _Ref38090148 \h Normalled connections, establishing a usable default routing allowing some work to be done without the necessity of a large number of patch cords for a basic signal path.  Several well known examples, all from the 1970s, are the ARP 2600, EML Electrocomp 101, and EMS VCS3 (the latter used a  REF _Ref41464925 \h Pin Matrix for routing rather than patch cords).  
Sequencer
A device which generates control signals telling a synth what notes to play, as well as other performance or setup information such as the application of pitch bend.  Sequencers first appeared in the 1960s; these devices generated a very short repeating pattern of control voltages for notes (typically 8 or 16), all set by tuning knobs; they were expensive and temperamental beasts, and not very flexible.  Sequencers with digital memory first appeared in the 1970s (the canonical example was the EMS Synti-AKS with its microprocessor-controlled sequencer built into the case lid), and these quickly evolved to be able to store longer and more complex patterns as well as additional performance information.  In the 1980s, synth manufacturers began including sequencers in some of their synth designs, and equipping them with  REF _Ref35841199 \h MIDI so that one sequencer could easily control multiple devices.  However, in 1985, the Voyetra company introduced the first sequencing software for the IBM PC, and at this point sequencers divided into two categories: those implemented inside of hardware (either built into a synth or as a separate box), and those implemented purely in software running on a personal computer.  From this point software sequencers have evolved considerably, with most now possessing abilities such as synchronizing with tape machines, hard disk audio recording and mixing, and ability to load  REF _Ref38090765 \h Patches and parameter settings as well as basic sequencing.  In fact, the more advanced applications such as Pro Tools have totally replaced both mixing boards and analog tape recorders in many studios.  Hardware-based sequencers haven’t evolved as quickly, but this type still has its adherents; they sometimes have better timing accuracy and usability advantages over the software sequencers.  
Shift Register

Sine Wave
A waveform that, when viewed on an oscilloscope, appears as a series of rounded “hills” and “dales”.  Sine waves are the “purest” waves, in the harmonic sense, because they consist solely of a single frequency with no overtones (a  REF _Ref35840291 \h Fourier Transform of a sine wave results in a single data point).  Audibly, a sine wave is not very interesting to the ear due to the lack of timbre caused by not having any harmonics.  Sine waves are used in synths mostly as reinforcement for other signals, for  REF _Ref38091064 \h Additive Synthesis, or as control signals.  
Slew Rate
The rate at which a signal increases or decreases with respect to time.  (Mathematically, it is the slope of the signal trace at a given point.)  Placing an upper limit on the slew rate, called slew rate limiting, is considered a form of distortion when it occurs in an amplifier.  However, in synthesis, slew rate limiting is often done intentionally as a form of  REF _Ref72920440 \h Wave Shaping.  Most often this is done to control signals to limit the rate at which the associated parameter can change, such as when a  REF _Ref72920547 \h Lag Processor is used to limit the frequency control voltage from a keyboard to produce  REF _Ref39587977 \h Portamento.  When applied to audio signals, slew rate limiting produces an effect aurally (but not mathematically) similar to a  REF _Ref72920640 \h Low Pass Filter.
SMPTE
An acronym standing for “Society of Motion Picture and Television Engineers”.  However, in the context of electronic music, it nearly always refers to a standard developed by that body for a time synchronization code.  
Soft Synth

Soft Thru
A capability of most  REF _Ref38201901 \h Sequencers that allows incoming  REF _Ref35841199 \h MIDI data to be routed to an arbitrary destination.  A performer who is recording with a sequencer has a need to be able to hear what he/she is playing while recording (or practicing, or experimenting with  REF _Ref38090765 \h Patches, etc.).  If the sequencer did not have Soft Thru capability, it would be necessary for the user to disconnect and re-connect MIDI cables and change  REF _Ref38206176 \h Channel assignments each time a different synth was needed.  With Soft Thru, the sequence can re-route the data to a different interface and re-map the channel numbers so that the data goes only to the desired synth and channel.  In such a setup, usually the source of the MIDI data is either a  REF _Ref38203151 \h Master Keyboard or a synth being used as a master keyboard with  REF _Ref40073231 \h Local Control turned off; often the sequencer will set up Soft Thru automatically depending on which track is selected for recording.
Song Position Pointer

Spectrum Analyzer
A device that displays how much energy an input waveform has at different wavelengths.  The classic spectrum analyzer used a narrow bandpass filter that swept through the audio range, graphing the level of signal that passed through the filter at different frequencies.  These devices were accurate but slow; they were not capable f accurately measuring a changing waveform.  In the late 1970s, the first “real-time” analyzers were developed, using banks of bandpass filters tuned at specific intervals (typically one octave or 1/3 octave apart) and using an array of indicator lights to display the results in bar-graph style.  Most current spectral analyzers use  REF _Ref36032284 \h Fast Fourier Transform to perform the analysis.  
Soft Synth
A synthesizer implemented entirely in software, which runs on a personal computer.  
Spring Reverb
A type of electromechanical  REF _Ref41460442 \h Reverb device.  It produces a reverb effect by inducing sound vibrations at one end of a long wire (which is coiled into a spring shape to reduce the amount of space it takes up, hence the name).  Another transducer at the far end picks up the vibrations.  As the waves reflect back and forth from one end of the spring to the other, and back, a reverb effect is produced.  Spring reverbs are often criticized for their harsh, trebly sound (and susceptibility to external vibration), but they are inexpensive to build and have been used in the past in many highly regarded keyboards such as the Hammond B-3 organ and the ARP 2600 synth.  
Square Wave
A waveform that alternates between two values, spending an equal amount of time at each value.  On an oscilloscope, the square wave looks just like its name: a series of squares (each with one side missing).  Performing a  REF _Ref35840291 \h Fourier Transform on a square wave reveals that it consists of a series of all of the odd-numbered harmonics of the fundamental frequeny.  As an audio signal, an unfiltered square wave has a pleasingly rounded, somewhat nasal yet mellow sound; different types of filtering yields a variety of useful sounds.  See also pulse wave.
SSM
An acronym for Solid State Microelectronics, one of two companies that in the mid-‘70s designed and sold an analog synthesizer-on-a-chip IC (see also  REF _Ref41460810 \h Curtis Chips).  SSM chips were used in many late-‘70s and early-‘80s polyphonic analog synths, including the Oberheim models of the day, and the rev 1 and 2 Prophet-5s.  Connoisseurs of such things consider the SSM chips to produce a “thicker” and “ballsier” sound than the Curtis design, but the SSMs had some reliability problems and by 1985 most designers that were still specifying these types of ICs had switched to Curtis.  The SSM designs had their roots in a specification originally drawn up by E-mu, and that company collected royalties on the sales for a time.  
Standard MIDI FIle
A standard way of storing  REF _Ref35841199 \h MIDI data in a disk file, such that the data can be exchanged between dissimilar brands and models of  REF _Ref38201901 \h Sequencers.  Several types of Standard MIDI Files exist: [need info on the types].
Step Entry
A mode of recording notes provided by many  REF _Ref38201901 \h Sequencers as an alternative to playing and recording the part in real time.  In step entry, a starting point and note value is chosen, and then the user begins playing notes (either on a real keyboard or by clicking the mouse on a graphic of a keyboard on a computer screen).  Each time a note is chosen, a note of the chosen pitch and value is entered in the score, and then the insert point is moved forward in time an amount equal to the note value (e.g, if the score is in 4/4 time and the chosen note value is half notes, the insert point will move two beats each time a note is entered).  Some step editors have provisions allowing entry of block chords.  Step entry is a form of Quantization and is often criticized for that reason, but it has its uses for entering complicated parts, and it is sometimes the only method of composition available to musicians who have physical disabilities.
String Synth

Stuck Note
A note that will not stop sounding, even after the performer lets up the key that sounded it.  This may result from a  REF _Ref38090765 \h Patch error such as setting an excessively long release time on an envelope generator, or accidentally bypassing a VCA such that an ungated  REF _Ref38088628 \h Oscillator output signal is connected directly to the synth’s main out.  More commonly, in a  REF _Ref35841199 \h MIDI setup, it results from the receiving device failing to receive a  REF _Ref36033058 \h Note Off message due to a communication problem or  REF _Ref38201901 \h Sequencer error (see  REF _Ref38091154 \h All Notes Off).
Subharmonic

Suboscillator

Sustain
(1) A phase of the output signal of the signal produced by an  REF _Ref42917501 \h Envelope Generator, in which the signal level is held constant.  Unlike the other conventional phases (see  REF _Ref42917650 \h ADSR), the sustain phase lasts an indefinite amount of time; it begins after the previous  REF _Ref42917886 \h Attack and  REF _Ref42917902 \h Decay phases have ended, and lasts as long as the performer holds the key down.  (2) When discussing conventional instruments, “sustain” is the amount of time between the start and end of the sound.  This can be applied to percussive instruments such as guitar, piano, or drums.  However, in electronic music terms, sustain is strictly the amount of time that the volume level holds (more or less) steady after initiation of the sound; by this definition percussive instruments have a sustain time of zero (they proceed immediately to the  REF _Ref42917936 \h Release phase after the initial attack and decay).  Under this definition, only instruments such as organs, bowed strings, woodwinds and brass have sustain.  
Sustain Pedal
(1) An electric switch, packaged in the form of a foot pedal, that is connected to a synth to act somewhat like the sustain pedal of a piano.  While the pedal is held down, any notes that are played by the performer are sustained.  Unlike a piano, on most synths the sustain pedal doesn’t just lengthen the amount of time it takes for the notes to fade away (the Release phase), it actually causes the notes to sustain indefinitely until the pedal is let up.  ( REF _Ref41461486 \h Voice Assignment may change this if too many notes are played.)  (2) A  REF _Ref35841199 \h MIDI  REF _Ref36141523 \h Controller message that corresponds to the action of the sustain pedal, assigned to controller type 64.  Although the message takes a standard 7-bit control value, the MIDI standard says that it is to be interpreted as a discrete switch; a value of zero corresponds to “off” and any non-zero value corresponds to “on”.  (Conventionally, a value of 127 ⎯ all 1 bits ⎯ is used for “on”.)
Synchronization

Synth Weighting
A method of contstructing a keyboard so that it has a moderately light and somewhat damped touch (and perhaps less key travel), somewhat like an organ.  Such a keyboard tends to be more suitable to players who have either trained on organ or never played keyboard prior to taking up synthesizers.  Piano-trained players often scoff at synth-weighted keyboards, but this type of keyboard can actually play faster, and it is usually less mechanically complicated.  See also  REF _Ref39932484 \h Piano Weighting.
System Exclusive
(Often abbreviated “sysex”) A  REF _Ref35841199 \h MIDI message type that allows manufacturers and implementers to add their own message types to extend the MIDI standard in any manner desired.  A system exclusive message is enclosed by start and end codes; it contains a manufacturer ID and unit number, and the format and content of the remainder is up to the implementer.  Each manufacturer is assigned an ID code by the MIDI Manufacturer’s Association.  System exclusive messages are often used for control functions which are not specified as standard  REF _Ref36141523 \h Controller messages, and for data transfers to/from a  REF _Ref38201901 \h Sequencer or  REF _Ref39589864 \h Patch Librarian.  (For example, many synth models use system exclusive messages to load and store  REF _Ref38090765 \h Patch data.)  Because manufacturers are free to define their own system exclusive message formats, these formats are not specified in the MIDI standard; it is necessary to read the manual or documentation for the particular synth of interest to discover its system exclusive message formats (assuming that the manufacturer has bothered to document it).  
TDM

Theremin
A early-20^th-century electronic instrument which generated tones via heterodyning (a process involving interference between two radio-frequency signals such that an audio-frequency signal is produced; see  REF _Ref46131848 \h Intermodulation).  The unique aspect to the theremin is the manner in which it is played; two loop antennas protrude from the instrument, one for each of the player’s hands.  Each antenna can sense the distance between itself and the hand.  One plays the instrument by moving the hands back and forth near and around the antennas; the performer never actually touches the instrument!  Typically one antenna controls frequency and the other controls volume.  In the hands of a skilled performer, the instrument produces a characteristic etherethral “singing” tone (augmented by generous helpings of vibrato), and was frequently used for movie soundtracks in the 1950s.  Theremins are still produced by several companies and craftsman (including Bob Moog, who has built them as a hobby since prior to building his first synth).  Some modern theremins generate MIDI data instead of tones and are used as  REF _Ref38203151 \h Master Keyboards.
Tick-Tock
Music played from a  REF _Ref38201901 \h Sequencer where the notes have been subject to  REF _Ref40074776 \h Quantization such that all the notes are exactly on the beats and (usually) have precise  REF _Ref36034039 \h Velocity and duration values.  
Time Code

Time Stretch
An effect in which the amount of time that a sound takes to play from start to finish is increased or decreased (as if a tape were being sped up or slowed down), but without altering the pitch.  Some  REF _Ref36140518 \h Samplers provide this as an effect that can be applied in non-real-time to a  REF _Ref36140582 \h Sample, for the purpose of tuning the sample’s length to an exact beat length, or just for the effect.  It may sound preposterous to try to perform a time stretch in real time, but some radio stations actually use devices that do just this (so that the music takes up less time, leaving more time for commercials); they start playing in an hour’s worth of program material at ten minutes prior to broadcast time, and over the hour the device “catches up” until at the end of the hour the input and output are in real time.
Tone Wheel
An electromechanical signal-generating device that uses a metal plate cut in the shape of a polyhedron or gear, and spun on a shaft.  A magnetic pickup is mounted near the edge of the plate, and as the bumps and variations in the plate shape pass by, they induce a signal in the pickup.  By far the best-known device employing tone wheels is the  REF _Ref39932600 \h Hammond Organ.
Tremolo
A regular repeating variation in the volume, or amplitude, of a signal.  In a synth, tremelo is accomplished by routing the signal to be modified through a  REF _Ref38202304 \h Voltage-Controlled Amplifier, and using a low-frequency oscillating signal to control the amplifier.  Tremelo is often confused with  REF _Ref41462883 \h Vibrato, but they are not the same thing.
Triangle Wave
A waveform that rises at a constant rate to a maximum value, and then declines at the same rate (in the other direction) to a minimum value, and then the cycle repeats.  On an oscilloscope, the triangle wave is a series of alternating slanted lines (or, for those of a certain generation, like the top of a Jughead hat).  
Unison
A mode provided by some  REF _Ref38124932 \h Polyphonic synths in which, whenever a key is pressed, every  REF _Ref39590529 \h Voice plays that note simultaneously.  Depending on what type of voice circuitry the synth uses, this can produce a very thick, heavy and dark sound.  
USB

VA
A  REF _Ref48024667 \h Virtual Analog synth or technology.  
VCA
See  REF _Ref38202304 \h Voltage-Controlled Amplifier.
VCF
See  REF _Ref38202333 \h Voltage-Controlled Filter.
VCO
See  REF _Ref38091874 \h Voltage-Controlled Oscillator.
Vector Synthesis

Velocity
A measure of how rapidly and forcefully a key on a keyboard is pressed when the player initially presses the key.  Velocity measurement is intended to simulate the behavior of a piano mechnism; a note struck on a piano is louder if the key is struck more forcefully.  (There are other changes in the note sound of a piano as the velocity varies, but such is beyond the scope of this definition.)  In the  REF _Ref35841199 \h MIDI standard, a velocity value is transmitted with each  REF _Ref36033860 \h Note On message.  All but a few of the synths manufactured since the original MIDI specification was published have supported velocity, although some older synths with retrofits do not.  Compare with aftertouch.  
Vibrato

Virtual Analog
A digital synth that has been programmed with software to (more or less) emulate the functionality and sounds of analog synths.  Virtual analogs first appeared in the late ‘90s, as performers sought to re-create the sounds of the classic analog synths.  Virtual analogs have the virtues that they are considerably less expensive, less bulky, and less maintenance-intensive than the analog synths they emulate, and their digital underpinnings allow them to offer functions that the old analogs didn’t have, such as patch memory and extensive polyphony.  However, considerable debate rages among analog purists as to how well the VA synths actually accomplish the primary objective of sounding like analog synths.  
Vocoder

Voice
In general, in a  REF _Ref38124932 \h Polyphonic synth, the collection of circuitry necessary to play a single note.  The number of voices available is equivalent to the number of notes that the synth can play simultaneously.  Some newer synths have a capability which allows two or more voices to be assigned to play a note simultaneously, using different  REF _Ref38090765 \h Patch settings, to produce layered effects; the tradeoff is that the polyphony available is reduced.  (For example, if the synth has 12 voices but a patch using two voices per note is created, then only 6 notes can be played simultaneously.)
Voice Assignment
The algorithm that a  REF _Ref38124932 \h Polyphonic synth uses to decide two things: (1) when a chord is played, which  REF _Ref39590529 \h Voice circuits to assign to which notes, and (2) how to handle the situation when the performer plays more notes than the synth has voice circuits available.  The latter is particularly problematic with polyphonic synths not equipped with a great number of voices, and no one best answer has ever been found.  Two common algorithms are “first note priority”, in which the new notes are ignored, and “last note priority” in which a held note that has been sounding for a long time has its voice “stolen” from it (the note is cut off abruptly so that the voice can be assigned to the new note).  Surprisingly, only a very few synths provide the performer with a choice of voice assignment algorithms (one is the Roland Juno-106).  
Voltage Control

Voltage-Controlled Amplifier
A circuit that increases or decreases the output level of an input signal according to the voltage level of a control signal.
Voltage-Controlled Filter
A  REF _Ref36446120 \h Filter that varies its  REF _Ref36446246 \h Cutoff Frequency according to the voltage level of a control signal.
Voltage-Controlled Oscillator
An  REF _Ref38088628 \h Oscillator that varies the frequency of its output signal according to the voltage level of a control signal.  
Volts/Hz
A standard for interpreting the control signal input to a VCO or VCF.  In the volts/Hz standard, a given change in the input voltage produces a change in the cycles/second value (Hz) of the circuit.  For example, if a 1V input results in a 1000Hz setting, then 2V yields 2000HZ, 3V yields 3000 Hz, 4V is 4000Hz, and so on.  The volts/Hz method is easier to implement in hardware than the volts/octave method, but it has two main faults.  Since the scaling doesn’t correspond to musical octaves, in order to be useful each source of control voltage has to be capable of varying intervals ⎯ for instance, if you have a control voltage and you want to raise it an octave, the amount by which you have to increase it depends on its present value.  Also, the volts/Hz method can, if large intervals are used, result in the use of rather high voltages to represent the higher frequencies.  This can be dangerous, and it also causes difficulties with power supply design and circuit implementation (the upper limit for what most integrated circuits used in synths will tolerate is about ±20V).  
Volts/Octave
A standard for interpreting the control signal input to a VCO or VCF.  In the volts/octave standard, a given change in the input voltage produces a change in the circuit relative to musical octaves, in which a given note in each octave is double the cycles/second (Hz) of the same note in the octave below.  For example, if a 1V input results in a 1000Hz setting, then 2V yields 2000HZ, 3V yields 4000 Hz, 4V is 8000Hz, and so on.  Nearly all equipment which uses volts/octave adheres to the 1 volt per 1 octave standard shown here.  (The major exceptions are the classic EMS Synthi and VCS-3 models, which used values from 0.2 to 0.3 volts/octave, the Micromoog at about 0.9 volts/octave, and nearly everything built by EML, which used 1.2 volts/octave.)  The volts/octave method is more difficult to implement in hardware, but it is considered more musically useful and it does not have the voltage range problems that the volts/Hz method has.  
Wave Shaping

Wavetable

Wavetable Synthesis

White Noise
A type of  REF _Ref36143860 \h Noise signal.  Mathematically, white noise is described as a signal in which all possible instantaneous values of the signal are equally likely at any given time.  In audio terms, white noise is biased towards the frequencies at the top end of the spectrum; its power decreases at a rate of 3 dB/octave in the direction of the lower frequencies.  
Zipper Noise
(Also known as “zipper effect”) An audible stepping effect in a parameter that is being varied, caused by the parameter’s being quantizied with insufficient resolution or at an insufficient rate.  The classic example is that of a volume fader or slider that is being moved, causing the sound being effected to audibly step up and down in volume rather than fading in and out smoothly.  The phenomenon can also be heard in other parameters such as filter cutoff settings, pitch bends, etc.