FAQS> GLOSSARY> Glossary of Computer Music Terms Acoustics: The study of the physics of sound.   A/D Converter: A device that translates analog signals into digital form. The new form being more convenient for storage and manipulation of the sound now represented as a series of numbers.   Additive synthesis: Synthesis of a timbre by direct summation of its component frequencies.   Aliasing: The generation of (usually) unwanted harmonics in a sound caused by the wrapping of high frequencies around the Nyquist frequency.   Algorithm: A step-by-step procedure for accomplishing a task. Each step must be unambiguously defined resulting in a clear path to the resolution of a problem to be solved.   All-pass network: A device that recirculates a signal through a delay line. It is used as an element in a reverberator (see Reverberation).   Amplify: To increase the amplitude of a signal.   Amplitude:   Acoustics: The peak amount of atmospheric displacement (air pushed by speaker, for example) of a sound, measured in units of pressure (Newtons per square meter).   Computer music: Numerical value of any given sample in a signal. Amplitude response: In a filter, the ratio of the amplitude of the output signal to that of the input signal. The amplitude response most often varies with frequency.   Analog signal: A signal that varies continuously; that is, it has a value at every point in time. Opposite of digital.   Argument: A value supplied as input to a function.   Array: A set of values stored sequentially in computer memory.   ASCII: American Standard Code for Information Interchange. One standard convention for representing alphanumeric characters in binary form.   Assembly language: A low-level language that enables the programmer to express an algorithm as a sequence of specific machine instructions.   Attack: The very beginning of a sound. The segment of the envelope of a sound in which the amplitude rises from zero to its peak. Also called the "rise".   Attack time: The length (often meaured in milliseconds) of an attack.   Attenuation: The reduction of the amplitude of a sound or of a component of the sound.   Band-pass filter: A filter that allows frequencies within a specified region and eliminates frequencies both above and below that region. Its passband is characterized by a center frequency, a bandwidth, and a midband gain.   Band-reject filter: A filter that eliminates frequencies within a specified region and allows frequencies both above and below that region. Its passband is characterized by a center frequency, a bandwidth, and a midband gain.   Bandwidth:   A measure of the width of the passband or stopband of a filter.   A measure of the width of the frequency region occupied by the spectrum of a signal.   Beating: A noticeable and periodic reduction in the amplitude of a sound caused by the interference of closely tuned frequency components. i.e.: the beating sound heard when trying to tune string instruments. The faster the beating, the more out of "tune" you are.   Binary number: A number whose digits can assume one of two states, either a 1 or 0. Each digit has a value two times the value immediately to its right.   Bit: A single binary digit, either 1 or 0. Smallest unit of information recognized by a digital computer.   Byte: A group of 8 bits. A byte is capable of assuming 256 (2^8) unique values. A common measure of computer memory.   Carrier wave: The wave to which modulation is applied. The carrier wave is altered in sympathy with the modulating signal.   Cascade relation: The relationship between two devices where the output of the first is applied to the input of the second.   Cent: A unit of measure used in tuning. There are 1200 cents in an octave.   Center frequency: The frequency about which the passband of a filter is symmetrically disposed.   Chorus effect: The creation from a single voice of the percept of multiple voices in unison.   Clavier: A keyboard of the type found on a piano or organ.   Coefficient: A constant used to multiply a variable. In a filter algorithm, a set of coefficients determines the characteristics of the filter. In the algebraic expression of a transfer function for a waveshaper, a set of coefficients determines the spectrum of the shaped waveform.   Comb filter: A device that recirculates a signal through a delay line. It is used as an element in a reverberator. The amplitude response of a comb filter exhibits peaks and valleys that are equally spaced in frequency.   Component: A single frequency element found in a spectrum.   Composing program: A program that generates a musical score using algorithms and parameters supplied by the composer.   Computer-aided composition: One of a number of approaches in which the mathematical and logical powers of the computer are enlisted to assist in the expression of a composer's musical ideas.   Constant: A numeric value that does not change during the course of a program.   Continuous:   Characteristic of a signal in which every point on the waveform is smoothly connected to the rest of the waveform.   Characteristic of a random process where the results can fall anywhere within a range of values.   Cosine Wave: A sinusoidal waveform whose phase relative to the sine wave is 90 degrees.   CPU (Central Processing Unit): The portion of hardware in a computer which interprets instructions and then executes them. It is the heart of any computer system.   Critical band: A measure of the ability of the ear to discriminate adjacent tones. Critical band plays an important role in masking of tones, and in the perception of loudness and timbre. The width of the critical band varies with frequency.   CRT (Cathode Ray Tube): The device that is showing this to you now.   Cutoff frequency: The frequency that marks the transition from passband to stopband in a filter. It is normally defined as the frequency at which the signal is attenuated by 3 dB.   Cycle: One repetition of a periodic waveform. D/A converter: A device that transfers digital signals into analog signals.   Data: A collection of information.   Data converter: D/A converter or A/D converter.   Decay: That portion of the envelope of a sound in which the amplitude decreases from its steady-state value to zero.   Decibel (dB): A unit of relative measure used to compare the intensities of two signals on a logarithmic scale. Under certain conditions the decibel can be used to compare the amplitudes of two signals as well.   Diatonic: The collection of pitches in a major scale.   Digital: Characteristic of a system or device that handles information in numerical quantities.   Discrete: Discontinuous, or a limited value, not infinite.   Discrete summation formula: In sound synthesis, a mathematical relationship that expresses the sum of sinusoids in a compact form.   Disk: A peripheral device for storing large quantities of information. For example a hard drive.   Distortion index: A control on the amount of distortion, and hence the spectral content, produced by a waveshaping instrument. The distortion index generally has a large effect on the amplitude of the signal as well.   Distortion synthesis: A class of sound synthesis techniques, including frequency modulation, nonlinear waveshaping, and the explicit use of discrete summation formulae, in which a controlled amount of distortion is applied to a simple waveform. All distortion synthesis techniques have an index which controls spectral richness.   Doppler shift: The perceived change in frequency or pitch observed when a sound source and a listener are moving relative to each other.   Dynamic range: The range of amplitudes that can be represented in a system. Dynamic range is limited on the low end by the noise of the system and on the high end by the distortion.   Dynamics: The various indications in music notation for change of loudness level in a musical passage.   Editor: A computer program that enables the entry and modification of program text and data files in a computer.   Envelope: The shape of the amplitude variation during the course of a tone. A simple envelope consists of three segments: attack (rise), steady-state, and decay.   Envelope generator: A device or function for creating an envelope.   Execution: The performance of a set of program instructions by a computer.   FFT (Fast Fourier Transform): A numerical technique for determining the spectrum of a digital sound.   File: A collection of information stored on a computers disk. A file may contain a program, data, or both.   Filter: A device that passes certain frequencies and attenuates others. Four representative types are: low-pass, high-pass, band-pass, and band-reject.   Flanging: The process of combining a signal with a delayed version of itself and varying the amount of delay to produce a characteristic "swishing" effect.   Flow chart: A graphical representation of the logic of an algorithm or program. In instrument design, a flow chart shows the interconnections among the unit generators.   Foldover: See aliasing.   Formant: A peaking in the spectral envelope of a tone. A formant is caused by resonances in the instrument or voice. Formants make an important contribution to our perception of timbre.   FORTRAN (FORmula TRANslation): An algebraically oriented programming language suited for tasks that require a great deal of numerical calculation.   Fourier analysis: The process of breaking down a waveform into its component frequencies.   Fourier transform: The mathematical technique for changing the time-domain representation of a signal (its waveform) into a frequency-domain representation (its spectrum).   Frequency: The rate of repetition of a periodic waveform. It is measured in Hertz (Hz).   Frequency domain: A way of characterizing a signal in terms of its frequency components.   Frequency modulation (FM): The alteration of the frequency of a carrier wave by another signal called a modulating wave.   FM synthesis: The alteration or distortion of the frequency of one oscillator by a signal from a modulating oscillator. This produces a waveform with many more spectral components than the presence of only two oscillators might seem to imply.   Frequency response: In a filter, the ratio of the output signal to the input signal versus frequency. The frequency response consists of two parts: amplitude response and phase response.   Function:   Mathematics: A way of expressing the dependencies of the value of one quantity on the values of other quantities.   Computer languages: A section of code which produces an output or "return value" based on some number (including none) of input values.   Fundamental: Ordinarily the lowest component in a harmonic spectrum. Under most conditions, the perceived pitch of a tone is at the frequency of the fundamental.   Fusion: The perception of a group of tones or spectral components as a single acoustic entity.   Gain: In a device, the ratio of output amplitude to input amplitude. When the gain is greater than one, the signal is amplified.   Glissando: A continuous change of frequency, either up or down.   Graphics terminal: A data terminal with a CRT for display of line segments as well as alpha numeric characters. Graphics display often enhances the clarity of presentation of information to the user.   Hardware: The electronic equipment that forms a computer system.   Harmonic: A spectral component that is an exact integer multiple of the fundamental frequency.   Hertz (Hz): A unit of measure for frequency. It is equivalent to cycles per second.   High-pass filter: A filter that passes frequencies above a specified cutoff frequency and attenuates ones below it.   Impulse: A digital signal consisting of single positive input sample with all preceding and following samples equal to zero.   Impulse response: The waveform produced by a digital filter when excited by a an impulse.   Index of modulation: A measure of the amount of modulation, and thus the spectral richness, produced in a frequency-modulated instrument. See FM synthesis.   Initialization: In a sound synthesis program, the setting of parameter values prior to the actual process of calculating sample values.   Instruction: In a computer, a numerical code stored in memory that represents an operation for the computer to perform.   Instrument design: A synthesis algorithm for realizing a particular class of sounds.   Intensity: A measure of the power in a sound, expressed in Watts/m^2. Intensity is the primary physical correlate with the perceived loudness of a sound.   Interactive: Characteristic of a situation where the user and the computer program respond to each other's actions on an approximately real-time basis. Any live-performance situation is, by definition interactive.   Interface: The boundary or means of connection between two or more elements in a computer system. An interface can be between hardware devices, pieces of software, or a user and a computer system.   Integrated circuit: A large number of electronic devices fabricated on a small piece of silicon.   Interpolation: The process of finding values intermediate to specified values. The two most common methods of interpolation are linear and exponential.   Interval: The musical name for the ration in frequency between two tones. Pairs of tones separated by the same musical interval share a similar quality.   Inversion: The reversal of direction of a musical interval. For example, the inversion of the interval C/E-flat is C/A.   I/O (Input/Output): A class of devices that provide the means for communication between the computer and its users or other computer hardware.   Karplus-Strong algorithm: An instrument design in which a signal is recirculated around a delay line through a low-pass filter. The algorithm is relatively efficient and quite successful at simulating the sound of a plucked string.   Kilohertz (kHz): 1000 Hertz.   Language (computer): A rigidly defined set of conventions for expressing algorithms. Once transmitted to the computer, the encode algorithm is translated into machine instructions.   Linear:   Characteristic of a phenomenon which changes by the same amount over a given interval of time.   Characteristic of a signal processor in which a change in amplitude of the input signal produces a similar change in the amplitude of the output signal.   Linear prediction: In a sampled data system, the process of determining the relationships that enable the value of the next output sample to be calculated as a combination of previous output samples.   Localization: The process of synthesizing cues that create the auditory illusion of the placement in space of a sound source.   Logarithmic: Characteristic of a phenomenon where changes are perceived on the basis of the ratio of the change.   Lookup table: An array, such as a wave table used by an oscillator, containing precomputed values of a mathematical function. Its use can save a great deal of computer time because a program can simply retrieve values from the table instead of performing extensive calculations.   Loudness: The subjective response to the amount of acoustical power received by the ear.   Low-pass filter: A filter that passes frequencies below a specified cutoff frequency, and attenuates ones above it.   Markov process: A conditional random process in which the higher-order probabilities can be calculated as products of first order probabilities.   Masking: The reduction in sensitivity to amplitude due to the fatigue of neurons on the basilar membrane. This often causes softer tones to be covered up by "covered up" by louder ones.   Memory: The repository of both programs and data. It is divided into discrete units or locations which are distinguished by unique numerical addresses.   Microsecond (usec): One one-millionth (.000001) of a second.   Midband gain: The ration of output amplitude to input amplitude for a signal at the center frequency of a band pass filter.   Millisecond (msec): One one-thousandth (.001) of a second.   Mixer: A device for combining signals by adding them together.   Modulating wave: The signal which alters the carrier wave in some way. Used in FM synthesis.   Modulation: The alteration of the amplitude, frequency, or phase of a carrier wave in accordance with a modulating signal. The signal resulting from the modulation has a more complex spectrum than would be obtained by the simple addition of the carrier wave and the modulating wave.   Motive: A characteristic melodic/rhythmic fragment in a piece of music, out of which larger units such as phrases are made.   Musique Concrete: A form of tape or electronic music made from "concrete" i.e. recorded sounds. In most music concrete the recorded sounds are modified electronically from their original form.   Music 4: An influential language for sound synthesis created by Max V. Mathews at the Bell Laboratories in the early 1960's and exported to several other institutions.   Noise: Sound with a distributed spectrum. The most common form of noise is called white noise, which is basically a hissing sound.   Non-linear processor: A signal-processing device in which a change in the amplitude of the input signal does not produce a similar change in the amplitude of the output signal. This alters the waveform, and hence the spectrum, of a signal passing through it.   Non-linear synthesis: See waveshaping.   Nyquist frequency: In a digital sound system, the frequency at one-half the sampling rate. It is the theoretical upper limit to representation of frequency components in a digital system.   One over f (1/f) noise: Noise with a spectrum that rolls off directly with frequency.   On-line: Attached directly to a computer and operational. In computer music, it generally is used to indicate that the data converters can be accessed directly from the computer that calculates the sample values.   Onset: The time at which a tone begins.   Operating system (OS): An organized collection of software which provides many useful services to the users of a computer. It also controls the flow of work in the system.   Orchestra: A collection of computer instrument designs.   Oscillator: A device for generating a periodic waveform. Its two principal controls are amplitude and frequency of repetition of the waveform.   Overflow: The condition that occurs when the result of a mathematical operation exceeds the capacity of the format used for number representation.   Overtone: A spectral component above the fundamental.   Parallel connection: The relationship among devices where the same signal is applied to the inputs of all devices simultaneously. The outputs of the devices are combined to form a single signal.   Parameter: A value input to an algorithm which is used in calculation the output. In computer music, a parameter in the score can control an attribute of the sound produced by a computer instrument.   Partial: A spectral component of a sound. It may or may not be harmonic to the fundamental.   Passband: The frequency region in which a filter passes signals with little or no attenuation.   Period: The time occupied by one repetition of a periodic waveform.   Periodic wave: A signal comprised of repetitions of a waveform at a particular, fixed frequency.   Peripheral: A device connected to the CPU in a computer system. Peripherals are usually for user communication (data terminals, printers, etc.) or external memory (disks, tape drives, etc.).   Phase: A means of comparing the relative position in time of two waveforms or of marking a specific point on a waveform.   Pitch: The subjective response to a frequency.   Pole: A resonance. A filter that implements a pole causes a peak in the spectral envelope of a signal passing through the filter.   Polynomial: An algebraic expression that takes the form of the sum of a series of terms where each term consists of a coefficient multiplying a variable raised to a power.   Precedence effect: In the presence of the same sound from several sources, the phenomenon by which a listener attributes the location of the source on the basis of the sound that arrives first. This occurs even when subsequent sounds have higher amplitudes.   Probability: The likelihood of obtaining a given outcome of a random process. It is expressed as the ratio of number of occurrences of that outcome to the total number of results of the random process.   Probability density function: A mathematical expression that indicates the likelihood of a continuous random variable occurring within a range of values.   Program: A sequence of instructions to accomplish a specific task which can be executed by a computer.   Psychoacoustics: The study of the way humans perceive sound. It includes such subjective responses to sound as pitch, loudness, duration, timbre, and apparent location.   Pulse: A waveform with significant amplitude only during a relatively brief portion of its period. A pulse has a very rich spectrum.   Q: A measure of the selectivity of a filter. A filter with a high Q has a narrow bandwidth.   Random: Characteristic of a process that, under repeated observations with the same set of conditions, does not always produce the same results.   Random variable: A variable which takes on a value as the result of a random process. A random variable is discrete when it can take on only specific values; It is continuous when it can assume any value within a range.   Real-time: Characteristic of a process in which data is processed at the same rate as it is taken in or used. For example, a digital synthesizer is said to operate in real time when its calculation rate equals the sampling rate.   Recursive filter: A digital filter that determines the value of its current output sample on the basis of past output sample.   Resolution: The fineness to which a quantity can be represented in a digital system.   Resonance: A spectral peak, such as formant.   Reverberation (reverb): The multiple reflections of sound in a room causing sound to be heard after all sources have ceased.   Ring modulation: The process of combining two signals by multiplication. Ring modulation produces sidebands but suppresses both the carrier and modulating frequencies.   Rise time: The duration of the attack segment of the envelope of a tone.   Rolloff: The rate at which the attenuation of a filter increases in the stop band. Expressed in units of dB/octave.   Sample: A number representing the amplitude of a digital waveform at a particular point in time.   Sampling: The process of representing a waveform digitally by measuring its value at discrete points in time.   Sampling increment: In a digital oscillator, the amount added to the current phase to determine which location in the wave table to use next. The sampling increment is directly proportional to frequency.   Sampling rate: The number of samples per second used to represent a digital waveform.   Score: A list of musical events. Each event has attributes, or parameters, to describe it. Common parameters include designation of instruments to play, starting time, duration, frequency, and amplitude.   Score editor: A computer program that enables entry and modification of scores.   Score preprocessor: A computer program that enables the encoding of scores in a syntax that is easy to read and bears a strong, intuitive relation to the encoded music. The score pre-processor translates the code into the parameter list score format required by the music-synthesis language.   Serialism: A kind of music based on an ordered set of elements, such as a twelve-tone row. It often includes ordering of other elements, such as rhythm or dynamics.   Series connection: See Cascade.   Sideband: A product of modulation in which new frequencies are generated on either side (i.e., above and below in frequency) of a given frequency.   Signal: A temporal phenomenon, whether electrical or digital, that carries information. Often synonymous with waveform.   Signal processor: A device that modifies a signal passing through it. Signal-to-noise (S/N) ratio: A numerical comparison of the signal level to the noise level in a system.   Sine wave: A sinusoidal waveform whose phase is taken to be zero.   Sinusoid: A smooth waveform whose spectrum contains only one component frequency.   Software: Programs that can be executed by a computer.   Spectral envelope: The outline showing the distribution of acoustical energy with frequency. A spectral envelope can exhibit formant peaks.   Spectrum: The representation of a signal in terms of its frequency components. The spectrum determines the sound's timbre.   Steady-state: The portion of the envelope of a tone in which the amplitude remains relatively constant.   Steady-state analysis: The characterization of the response of a device, such as a filter, to a sinusoid that has been applied to the device long enough for the output of the device to settle to a constant response.   Steady-state response: The response of a filter to a constant periodic signal.   Stochastic process: See random.   Stopband: The frequency region in which filter provides the greatest amount of attenuation.   Subscore: A part of a score, such as a group of proximate notes. Some score editors enable operations on subscores.   Subroutine: Computer programming: A self-contained algorithm invoked from the main program or from within another subroutine.   Subtractive synthesis: A technique that uses filters to alter the spectral content of a sound.   Synthesis: The realization of electrically-generated acoustical elements.   Synthesizer: A device that implements synthesis algorithms, most often in real time.   Timbre: The characteristic tone quality of a particular sound or class of sounds.   Time domain: A way of characterizing a signal in terms of its amplitude fluctuations versus time. The representation of a signal in the time domain is called its waveform.   Transducer: A device that converts mechanical energy, such as a sound wave, into electrical signals. All manual input devices, including claviers, digitizing tablets, sliders, etc. are transducers.   Transfer function: In a non-linear processor, an expression that determines output values on the basis of input values.   Transposition: The raising or lowering, by a specified musical interval, of the frequency of musical tones.   Tuning: Any one of a number of systems for distributing, or mapping, musical intervals into frequency.   Twelve-tone music: Music based on a twelve-tone row; that is, on an ordering of all twelve chromatic pitches and various permutations of that ordering. See serialism.   Underflow: The condition that occurs when the result of a mathematical operation is too small to be accurately represented in the data format that is used. This phenomenon can occur, for example, when two nearly equal numbers are subtracted from each other.   Unit generator: An algorithm that performs a particular function of sound generation, modification, or combination. It is controlled by parameters obtained from a score or transducer.   Variable: In a computer program, a reference to a memory location whose value can change during the course of a program.   Vibrato: A perceptibly slow, quasi-periodic excursion both above and below the fundamental frequency of a tone.   Waveform:   Acoustics: The pattern of pressure variation versus time in a sound.   Computer Music: The pattern of samples versus time. The shape of the waveform can have a great effect on the perceived timbre.   Waveshaper: See non-linear processor.   Waveshaping: A technique of distortion synthesis which creates complex spectra from simple tones by systematically distorting the amplitude, and thus the shape, of the waveform.   Wave table: An array in which sequential values represent the successive samples in a single cycle of a waveform. Often used with oscillators.   White noise: Noise with a uniformly distributed spectrum. White noise has a "hissing" sound.   Zero: An anti-resonance point in a filter frequency response. A filter that implements a zero produces a dip in the spectral envelope of a signal at the zero point.