adaptive delta pulse code modulation (ADPCM): An audio compression algorithm for digital audio based on describing level differences between adjacent samples.
aliasing: Undesired frequencies that are produced when harmonic components of an audio signal being sampled by a digital recording device (or harmonic components 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.
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: Of, relating to, or being a mechanism in which data is represented by continuously variable physical quantities
analog-to-digital 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.
application: A sub-program in the Windows environment, such as VFEdit®, or Microsoft Word for Windows.
attenuate: To reduce the level of a signal.
b: An abbreviation for byte.
B: An abbreviation for bel.
batch process: A technique that permits more than one file or operation to be performed with a single command.
bel: Named for Alexander Graham Bell, who did the original scientific investigations; Also see decibel.
byte: A group of eight binary digits processed as a unit by a computer and used especially to represent an alpha-numeric character; also see word.
carrier: A signal that is modulated by some other signal, as in FM synthesis.
CCITT: Consultative Committee on International Telephone and Telegraph. The CCITT was an international standards committee now known as the ITU.
C-ITU: Committee of the International Telecommunication Union. The International Telecommunication Union (ITU) is group that sets international communications standards. They sponsor committees to provide detailed technical specifications for those standards.
clangorous: Sounds containing partials that are not part of the natural harmonic series. Clangorous tones often sound bell-like.
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 enables a device to achieve a greater apparent dynamic range with fewer bits per sample word.
cutoff frequency: The point in the frequency spectrum beyond which a synthesizer filter attenuates the audio signal being sent through it.
dB: See decibel.
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. To measure a signal in decibels, you need to know what level it is referenced to. Commonly used reference levels are indicated by such symbols as dBm, dBV, and dBu.
default: A selection automatically used by a computer program in the absence of a choice made by the user.
Dialogic: Trade name of a telephony board manufacturer.
digital: Relating to an audio recording method in which sound waves are represented digitally (as on magnetic disk) so that in recordings wow and flutter are eliminated and background noise is reduced; also see analog. (Informal definition: Digital sound is what you get when you electronically chop up a continuous analog sound.)
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 DAC at their outputs to create audio signals.
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; also see wet.
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 echo is a typical DSP function.
DSP: See digital signal Processing.
feedback: See resonance.
fast Fourier transform : A quick method of performing a Fourier analysis on a sound; see Fourier analysis.
FFT: See fast Fourier transform.
file format: A description of the disk file format or contents; also see pure, indexed, wave.
file type: A description of the disk file format or contents; also see pure, indexed, wave.
filter: 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.
FM: 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 sounds.
Fourier analysis: A technique, usually performed with a digital signal processing (DSP) algorithm, that allows complex dynamically changing audio waveforms to be described mathematically as sums of sine waves at various frequencies and amplitudes; also see DSP.
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. When the modulation wave is in the audio range (above 20 Hz, or so) FM is perceived as a change in tone color. FM synthesizers, commonly found on sound cards, create sounds using audio-range frequency modulation.
G: for giga, i.e., a billion, as in 1 GHz = 1,000,000,000 (109) hertz, or Gb, a billion bytes; [both 'g' in giga are pronounced as in 'go', not as in jelly].
direct-to-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 440 Hz, the first two harmonics are 880 Hz and 1,320 Hz (1.32 kHz). See overtone; also see inharmonic.
headroom: The amount of additional signal above the nominal input level that can be sent into a module before clipping distortion occurs.
hertz: A unit of frequency equal to one cycle per second. Named for Heinrich R. Hertz who did the original scientific investigations.
high-pass filter: A filter that attenuates the frequencies below its cutoff frequency.
Hz: abbreviation for hertz
indexed file: A file format that permits you to group related audio segments, then access those segments by specifying an index number.
inharmonic: Containing frequencies that are not whole-number multiples of the fundamental; also see harmonic.
interactive voice response (IVR) : Computer systems that answer (or dial) a phone, play or record a message, often under control of the user's touch-tone phone. A voice mail system is an example of a basic IVR system.
IRQ: Interrupt Request
ITU: International Telecommunication Union. A group that sets international communications standards. The ITU was previously known as the CCITT.
k: abbreviation for kilo (thousand): 1,000 or 103, as in 1 kHz.
low-frequency oscillator (LFO) : An oscillator whose output is below the audible frequency range, typically used as a control source for modulating the sound to create vibrato, tremolo, trills, and so on.
m: abbreviation for milli (one thousandth): 1/1000 or 10-3, as in 1 mW (0.001 W).
M: abbreviation for mega (million): 1,000,000 or 106, as in 1 MHz.
Nyquist frequency: The highest frequency that can be reproduced accurately when a signal is digitally encoded at a given sample rate. Theoretically, the Nyquist frequency is half of the sampling rate. For example, when a digital recording uses a sampling rate of 11 kHz, the Nyquist frequency is 5.5 kHz. If a signal being sampled contains frequency components that are above the Nyquist limit, aliasing will be introduced in the digital representation of the signal unless those frequencies are filtered out prior to digital encoding; see aliasing, low-pass filter.
OEM: Original equipment manufacturer. A company that produces an end product as opposed to a sub-assembly.
oscillator: An electronic sound source. In an analog synthesizer, oscillators typically produce regularly repeating fluctuations in voltage-that is, they oscillate. In a digital synthesizer, an oscillator more typically plays back a complex waveform by reading the numbers in a wavetable.
overtone: A whole-number multiple of the fundamental frequency.
frequency of a tone: The overtones define the harmonic spectrum of a sound. See Fourier analysis; also see partial.
partial: One of the sine-wave components (the fundamental, an overtone, or a tone at some other frequency) of a complex tone; see overtone.
PC: Personal computer.
pole: A portion of a filter circuit. The more poles a filter has, the more abrupt its cutoff slope will be. Each pole causes a slope of 6 dB per octave; typical filter configurations are two-pole (12 dB/oct) and four-pole (24 dB/oct). See rolloff.
pot: See potentiometer.
potentiometer : A device used to adjust 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 also be either hardware or "virtual sliders" on a computer display.
prompts: Common term for outgoing messages recorded for your voice messaging system. These messages typically "prompt" the user to press a key for a specific person or service.
pure file: Files containing only the digitized sound.
Q: See resonance.
quantization noise: One of the types of errors introduced into an analog audio signal by encoding it in digital form. The digital equivalent of tape hiss, quantization noise is caused by the small differences between the actual amplitudes of the points being sampled and the bit resolution of the analog-to-digital converter.
quantized: Set up to produce an output in discrete steps.
reconstruction filter: A low-pass filter on the output of a digital-to-analog converter that smoothes the staircase-like changes in voltage produced by the converter in order to eliminate clock noise from the output.
regeneration: See resonance; feedback.
resonance: A function of a filter in which a narrow band of frequencies (the resonant peak) becomes relatively more prominent. If the resonant peak is high enough, the filter will begin to oscillate, producing an audio output even in the absence of input. Filter resonance is also known as emphasis, and as Q. It is also referred to in some older instruments as regeneration or feedback, because feedback was used in the circuit to produce a resonant peak.
rolloff slope: The acuity of a filter cutoff frequency. Rolloff is generally measured in decibels (dB) per octave. A shallow slope, such as 6 dB per octave, allows some frequency components beyond the cutoff frequency to be heard, but at a reduced volume. When the rolloff slope is steep (on the order of 24 dB/oct), frequency components very close to the cutoff frequency are reduced in volume so much that they fall below the threshold of audibility. See filter, and pole.
SDK: Software development kit.
sidebands: Frequency components outside the natural harmonic series, generally introduced to the tone by using an audio-range wave for modulation. See clangorous.
sine wave: A signal put out by an oscillator in which the voltage, or equivalent, rises and falls smoothly and symmetrically, following the trigonometric formula for the sine function. Sub-audio sine waves are used to modulate other waveforms to produce vibrato and tremolo. Audio-range sine waves contain only the fundamental frequency, with no overtones, and thus can form the building blocks for more complex sounds.
sound card: Add-on hardware typically placed inside the computer and used to record and play digital audio. These devices usually interface to standard audio equipment such as microphones and speakers.
telephony card: Add-on hardware typically placed inside the computer and used record and play digital audio. These devices usually interface to standard telephone lines and often can handle multiple phone lines per board; also see voice board.
total harmonic distortion (THD) : An audio measurement specification used to determine how accurately a device can reproduce an input signal at its output. THD describes the cumulative level of the harmonic overtones the device being tested adds to an input sine wave. THD+n is a specification that includes both harmonic distortion of the sine wave and nonharmonic noise.
TI\F DLL: VISI's Telephone Interface Dynamic Link Library.TI/F DLL is a set of programs that manage the telephony audio Terminate-and-Stay-Resident (TSR) driver and enables it to communicate with other Windows programs.
transient: Any of the non-sustaining, non-periodic frequency components of a sound, usually of brief duration and higher amplitude than the sustaining components, and occurring near the onset of the sound (attack transients).
tremolo: A periodic change in amplitude, usually controlled by an LFO, with a periodicity of less than 20 Hz; also see vibrato.
vap: A common file extension specifying an indexed file format. Typically encountered as FILENAME.VAP
VBase: A type of indexed files containing raw audio data plus additional format, control, and annotation information. These files permit you to group related audio segments, then access those segments by specifying an index number.
vibrato: A periodic change in frequency, often controlled by an LFO, with a periodicity of less than 20 Hz; also see tremolo.
VISI: Voice Information Systems, Inc. The really great company that makes this product.
voice board : Add-on hardware typically placed inside the computer and used record and play digital audio. These device usually interface to standard telephone lines and often can handle multiple phone lines per board; also see telephony card.
vox: A file extension specifying a generic telephony audio format. Typically encountered as FILENAME.VOX
wav: A file extension specifying an industry standard multimedia audio format. Typically encountered as FILENAME.WAV
wave: An industry standard file format that contains raw audio data plus additional format, control, and annotation information.
waveform: A signal, either sampled (digitally recorded) or periodic, being generated by an oscillator. Also, the graphic representation of this signal, as on a computer screen. Each waveform has its own unique harmonic content. See oscillator.
wet: Consisting entirely of processed sound. The output of an effects device is 100% wet when only the output of the processor itself is being heard, with none of the dry (unprocessed) signal; also see dry.
word: A number of bytes processed as a unit and conveying a quantum of information in communication and computer work. Also, a single number (sampled word) that represents the instantaneous amplitude of a sampled sound at a particular moment. In 8-bit recording, a sample word contains one byte; in 16-bit recording, each word is a two-byte number.