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Glossary of Electronic Music Terms

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A ADC: See analog-to-digital converter.

A/D converter: See analog-to-digital converter.

ADPCM: Adaptive delta pulse code modulation. An audio compression algorithm for digital audio based on describing level differences between adjacent samples.

ADSR: Attack/decay/sustain/release, the four segments of a common type of synthesizer envelope. The controls for these four parameters determine the duration (or in the case of sustain, the height) of the segments of the envelope. See envelope.

aftertouch: A type of control data generated by pressing down on one or more keys on a synthesizer keyboard after they have reached and are resting on the keybed. See channel pressure, poly pressure.

AIFF: Audio interchange file format. A common Macintosh audio file format. It can be mono or stereo, at sampling rates up to 48kHz. AIFF files are QuickTime compatible.

algorithm: A set of procedures designed to accomplish something. In the case of computer software, the procedures may appear to the user as a configuration of software components -- for example, an arrangement of operators in a Yamaha DX-series synthesizer -- or as an element (such as a reverb algorithm) that performs specific operations on the signal.

algorithmic composition: A type of composition in which the large outlines of the piece, or the procedures to be used in generating it, are determined by the human composer while some of the details, such as notes or rhythms, are created by a computer program using algorithmic processes.

aliasing: Undesired frequencies that are produced when harmonic components within the audio signal being sampled by a digital recording device or generated within a digital sound source lie above the Nyquist frequency. Aliasing differs from some other types of noise in that its pitch changes radically when the pitch of the intended sound changes. See Nyquist frequency.

all-notes-off: A MIDI command, recognized by some but not all synthesizers and sound modules, that causes any notes that are currently sounding to be shut off. The panic button on a synth or sequencer usually transmits all-notes-off messages on all 16 MIDI channels.

amplitude: The amount of a signal. Amplitude is measured by determining the amount of fluctuation in air pressure (of a sound), voltage (of an electrical signal), or numerical data (in a digital application). When the signal is in the audio range, amplitude is perceived as loudness.

analog: Capable of exhibiting continuous fluctuations. In an analog audio system, fluctuations in voltage correspond in a one-to-one fashion with (that is, are analogous to) the fluctuations in air pressure at the audio input or output. In an analog synthesizer, such parameters as oscillator pitch and LFO speed are typically controlled by analog control voltages rather than by digital data, and the audio signal is also an analog voltage. Compare with digital.

analog-to-digital (A/D) converter (ADC): A device that changes the continuous fluctuations in voltage from an analog device (such as a microphone) into digital information that can be stored or processed in a sampler, digital signal processor, or digital recording device.

attack: The first part of the sound of a note. In a synthesizer envelope, the attack segment is the segment during which the envelope rises from its initial value (usually zero) to the attack level (often the maximum level for the envelope) at a rate determined by the attack time parameter.

attenuator: A potentiometer (pot) that is used to lower the amplitude of the signal passing through it. The amplitude can usually be set to any value between full (no attenuation) and zero (infinite attenuation). Pots can be either rotary or linear (sliders), and can be either hardware or "virtual sliders" on a computer screen.

auto-correct: See quantization.

B

bandwidth: The available "opening" through which information can pass. In audio, the bandwidth of a device is the portion of the frequency spectrum that it can handle without significant degradation. In digital communications, the bandwidth is the amount of data that can be transmitted in a given period of time.

bank: (1) A set of patches. (2) Any related set of items, e.g., a filter bank (a set of filters that work together to process a single signal).

baud rate: Informally, the number of bits of computer information transmitted per second. MIDI transmissions have a baud rate of 31,250 (31.25 kilobaud), while modems typically have a much lower rate of 2,400, 9,600, or 14,400 baud.

bend: To change pitch in a continuous sliding manner, usually using a pitch-bend wheel or lever. See pitch-bend.

bit: The smallest possible unit of digital information, numerically either a 1 or a 0. Digital audio is encoded in words that are usually eight, 12, or 16 bits long (the bit resolution). Each added bit represents a theoretical improvement of about 6dB in the signal-to-noise ratio.

bpm: Beats per minute. The usual measurement of tempo.

brick-wall filter: A lowpass filter at the input of an analog-to-digital converter, used to prevent frequencies above the Nyquist limit from being encoded by the converter. See Nyquist frequency, aliasing.

buffer: An area of memory, used for recording or editing data before it is stored in a more permanent form.

bulk dump: See data dump.

byte: A group of eight bits. (MIDI bytes consist of ten bits because each byte includes a start bit and a stop bit, with eight bits in the middle to convey information.)

C

card: (1) A plug-in memory device. RAM cards, which require an internal battery, can be used for storing user data, while ROM cards, which have no battery, can only be used for reading the data recorded on them by the manufacturer. (2) A circuit board that plugs into a slot in a computer.

carrier: A signal that is being modulated by some other signal, as in FM synthesis.

CD-ROM: Compact disc read-only memory. A compact disc format that can store data other than just standard CD audio. Many programs, sound sample libraries, and graphics are distributed on CD-ROM because each CD can store hundreds of megabytes of information, yet costs about the same to manufacture as a floppy disk, which only stores about 1 megabyte. See ROM.

cent: The smallest conventional unit of pitch deviation. One hundred cents equal one half-step.

channel: An electrical signal path. In analog audio (such as a mixer), each channel consists of separate wired components. In the digital domain, channels may share wiring, and are kept separate through logical operations. MIDI provides definitions for 16 channels, which transmit not audio signals but digital control signals for triggering synthesizers and other devices.

channel pressure: A type of MIDI control message that is applied equally to all of the notes on a given channel; the opposite of poly pressure, in which each MIDI note has its own pressure value. Also called aftertouch, channel pressure is generated on keyboard instruments by pressing down on a key or keys while holding them down. See aftertouch, poly pressure.

chorusing: A type of signal processing. In chorusing, a time-delayed or detuned copy of a signal is mixed with the original signal. The mixing process changes the relative strengths and phase relationships of the overtones to create a fatter, more animated sound. The simplest way to achieve chorusing is to detune one synthesizer oscillator from another to produce a slow beating between them.

clangorous: Containing partials that are not part of the natural harmonic series. Clangorous tones often sound bell-like.

clock: Any of several types of timing control devices, or the periodic signals that they generate. A sequencer's internal clock is always set to some number of pulses per quarter-note (ppq), and this setting is one of the main factors that determine how precisely the sequencer can record time-dependent information. The actual clock speed is usually determined by the beats-per-minute setting. See ppq, bpm, MIDI clock.

clock resolution The precision (measured in ppq) with which a sequencer can encode time-based information.

companding: A type of signal processing in which the signal is compressed on input and expanded back to its original form on output. Digital companding allows a device to achieve a greater apparent dynamic range with fewer bits per sample word.

compression: (1) The process of reducing the amplitude range of an audio signal by reducing the peaks and bringing up the low levels. (2) The process of reducing a data file in size, often by noting patterns in the data and summarizing them. Some types of audio data compression are "lossy," meaning the quality of the audio is reduced.

continuous controller: A type of MIDI channel message that allows control changes to be made in notes that are currently sounding. See controller.

controller: (1) Any device -- for example, a keyboard, wind synth controller, or pitch-bend lever -- capable of producing a change in some aspect of a sound by altering the action of some other device. (2) Any of the defined MIDI data types used for controlling the ongoing quality of a sustaining tone. Strictly speaking, MIDI continuous controllers are numbered from 0 to 122; in many synthesizers, the controller data category is more loosely defined to include pitch-bend and aftertouch data.

crossfade looping: A sample-editing feature found in many samplers and most sample-editing software, in which some portion of the data at the beginning of a loop is mixed with some portion of the data at the end of the same loop, so as to produce a smoother transition between the end and the beginning when the loop plays.

cross-switching: A velocity threshold effect in a synthesizer in which one sound is triggered at low velocities and another at high velocities, with an abrupt transition between the two. If the transition is smooth rather than abrupt, the effect is called crossfading rather than cross-switching. Cross-switching can also be initiated from a footswitch, LFO, or some other controller. Also called velocity switching.

cutoff frequency: The point in the frequency spectrum beyond which a synthesizer's filter attenuates the audio signal being sent through it.

D

DAC: See digital-to-analog converter.

data dump: A packet of memory contents being transmitted from place to place (usually in the form of MIDI system-exclusive data) or stored to a RAM card.

daughterboard: A small circuit board that can be attached to a larger one (the motherboard), giving it new capabilities. For example, some companies manufacture daughterboards that add sampled sounds to soundcards that previously could only synthesize sounds via FM.

dB: See decibel.

decay: The second of the four segments of a typical ADSR envelope. The decay control determines the amount of time it takes for the envelope to fall from the peak reached at the end of the attack segment to the sustain level. See ADSR.

decibel: A unit of measurement used to indicate audio power level. Technically, a decibel is a logarithmic ratio of two numbers, which means that there is no such thing as a dB measurement of a single signal. In order to measure a signal in dB, you need to know what level it is referenced to. Commonly used reference levels are indicated by such symbols as dBm, dBV, and dBu.

delay: (1) The first stage of a five-stage DADSR envelope, which delays the beginning of the envelope's attack segment. (2) A control function that allows one of the elements in a layered sound to start later than another element. (3) A signal processor, used for flanging, doubling, and echo, that holds its input for some period of time before passing it to the output, or the algorithm within a signal processor that creates delay.

detune: Noun: A control that allows one oscillator to sound a slightly different pitch than another. Verb: To change the pitch of one oscillator relative to another, producing a fuller sound.

digital: Using computer-type binary arithmetic operations. Digital music equipment uses microprocessors to store, retrieve, and manipulate information about sound in the form of numbers, and typically divides potentially continuous fluctuations in value (such as amplitude or pitch) into discrete quantized steps. Compare with analog.

digital-to-analog converter (DAC): A device that changes the sample words put out by a digital audio device into analog fluctuations in voltage that can be sent to a mixer or amplifier. All digital synthesizers, samplers, and effects devices have DACs (rhymes with fax) at their outputs to create audio signals.

DirectX: This Microsoft Windows API was designed to provide software developers with direct access to low-level functions on PC peripherals. Before DirectX, programmers usually opted for the DOS environment, which was free of the limited multimedia feature set that characterized Windows for many years.

download: To transfer a file from another computer into your own. Often done by modem. See modem.

dry: Consisting entirely of the original, unprocessed sound. The output of an effects device is 100% dry when only the input signal is being heard, with none of the effects created by the processor itself. Compare with wet.

DSP: Digital signal processing. Broadly speaking, all changes in sound that are produced within a digital audio device, other than changes caused by simple cutting and pasting of sections of a waveform, are created through DSP. A digital reverb is a typical DSP device.

dump: see data dump.

dynamic voice allocation: A system found on many multitimbral synthesizers and samplers that allows voice channels to be reassigned automatically to play different notes (often with different sounds) whenever required by the musical input from the keyboard or MIDI.

E

early reflections: A reverb algorithm whose output consists of a number of closely spaced discrete echoes, designed to mimic the bouncing of sound off of nearby walls in an acoustic space.

echo: A discrete repetition of a sound, as opposed to reverberation, which is a continuous wash of closely spaced, non-discrete echoing sound. See delay (3), reverb.

edit buffer: An area of memory used for making changes in the current patch. Usually the contents of the edit buffer will be lost when the instrument is switched off; a write operation is required to move the data to a more permanent area of memory for long-term storage.

editor/librarian: A piece of computer software that allows the user to load and store patches and banks of patches (the librarian) and edit parameters (the editor).

effects: Any form of audio signal processing -- reverb, delay, chorusing, etc.

envelope: A shape that changes as a function of time. The shape of a synthesizer's envelope is controlled by a set of rate (or time) and level parameters. The envelope is a control signal that can be applied to various aspects of a synth sound, such as pitch, filter cutoff frequency, and overall amplitude. Usually, each note has its own envelope(s).

envelope generator: A device that generates an envelope. Also known as a contour generator or transient generator, because the envelope is a contour (shape) that is used to create some of the transient (changing) characteristics of the sound. See ADSR, envelope.

envelope tracking: A function (also called keyboard tracking, key follow, and keyboard rate scaling) that changes the length of one or more envelope segments depending on which key on the keyboard is being played. Envelope tracking is most often used to give the higher notes shorter envelopes and the lower notes longer envelopes, mimicking the response characteristics of percussion-activated acoustic instruments, such as guitar and marimba.

event editing: An operation in a sequencer in which one musical event at a time is altered.

F

FFT: Fast Fourier transform. A quick method of performing a Fourier analysis on a sound. See Fourier analysis.

filter: (1) A device for eliminating selected frequencies from the sound spectrum of a signal and perhaps (in the case of a resonant filter) increasing the level of other frequencies. See lowpass filter. (2) A device (MIDI filter) that eliminates selected messages from the MIDI data stream.

FM: See frequency modulation.

FM synthesis: A technique in which frequency modulation (FM) is used to create complex audio waveforms. See frequency modulation.

formant: A resonant peak in a frequency spectrum. For example, the variable formants produced by the human vocal tract are what give vowels their characteristic sound.

Fourier analysis: A technique, usually performed using a DSP algorithm, that allows complex, dynamically changing audio waveforms to be described mathematically as sums of sine waves at various frequencies and amplitudes. See DSP.

frame: The basic unit of SMPTE time code, corresponding to one frame of a film or video image. Depending on the format used, SMPTE time can be defined with 24, 25, 30, or 29.97 frames per second. See SMPTE time code.

FreeMIDI: A Macintosh operating system extension developed by Mark of the Unicorn that enables different programs to share MIDI data. For example, a sequencer could communicate with a librarian program to display synthesizer patch names -- rather than just numbers -- in the sequencer's editing windows.

frequency modulation (FM): A change in the frequency (pitch) of a signal. At low modulation rates, FM is perceived as vibrato or some type of trill, depending on the shape of the modulating waveform. When the modulating wave is in the audio range (above 20Hz or so), FM is perceived as a change in tone color. FM synthesizers, commonly found on computer soundcards, create sounds using audio-range frequency modulation.

G

gain: The amount of boost or attenuation of a signal.

General MIDI (GM): A set of requirements for MIDI devices aimed at ensuring consistent playback performance on all instruments bearing the GM logo. Some of the requirements include 24-voice polyphony and a standardized group (and location) of sounds. For example, patch #17 will always be a drawbar organ sound on all General MIDI instruments.

glide: A function, also called portamento, in which the pitch slides smoothly from one note to the next instead of jumping over the intervening pitches.

gigabyte: One billion (for British viewers, one thousand million) bytes.

global: Pertaining to or governing all of the operations of an instrument.

graphic editing: A method of editing parameter values using graphic representations (for example, of envelope shapes) displayed on a computer screen or LCD.

H

hard disk recording: A computer-based form of tapeless recording in which incoming audio is converted into digital data and stored on a hard disk.

harmonic: A frequency that is a whole-number multiple of the fundamental frequency. For example, if the fundamental frequency of a sound is 440Hz, then the first two harmonics are 880Hz and 1,320Hz (1.32kHz). See overtone.

headroom: The amount of additional signal above the nominal input level that can be sent into or out of an electronic device before clipping distortion occurs.

Hertz (Hz): the unit measurement of frequency. One Hz equals one cycle per second. The frequency range of human hearing is from 20Hz to 20kHz (20,000Hz).

highpass filter: A filter that attenuates the frequencies below its cutoff frequency.

Hz: See Hertz.

I

inharmonic: Containing frequencies that are not whole-number multiples of the fundamental. See harmonic.

interface: A linkage between two things. A user interface is the system of controls with which the user controls a device. Two devices are said to be interfaced when their operations are linked electronically. An interface box is often required to convert signals from one form to another. For example, in order to get MIDI data in and out of a computer, you need some type of MIDI interface hardware. This may hook to an existing port on the computer, such as the printer port, or (in the case of the IBM-PC) it may consist of a circuit board that is plugged into one of the computer's internal slots.

IRQ: Interrupt Request level. In IBM-PCs, a setting given to peripheral devices like soundcards and CD-ROM drives that identifies them to the computer's CPU. When the peripheral needs to communicate with the CPU, it will send an interrupt with that value. Problems will result if two or more peripherals are set to the same IRQ value.

J

K

keyboard scaling: A function with which the sound can be altered smoothly across the range of the keyboard by using key number as a modulation source. Level scaling changes the loudness of the sound, while filter scaling changes its brightness.

key follow: See envelope tracking.

keyboard tracking: See envelope tracking.

kHz: kilohertz (thousands of Hertz). See Hertz.

kilobyte (Kb): Linguistically speaking, a thousand bytes. In practice, a kilobyte generally contains 1,024 bytes.

L

layering: Sounding two or more voices, each of which typically has its own timbre, from each key depression. Layering can be accomplished within a single synthesizer, or by linking two synths together via MIDI and assigning both to the same MIDI channel.

LFO: Low-frequency oscillator. An oscillator especially devoted to applications below the audible frequency range, and typically used as a control source for modulating a sound to create vibrato, tremolo, trills, and so on.

librarian: See editor/librarian.

loop: A piece of material that plays over and over. In a sequencer, a loop repeats a musical phrase. In a sampler, loops are used to allow samples of finite length to be sustained indefinitely.

lowpass filter: A filter that attenuates (reduces in level) the frequencies above its cutoff frequency.

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