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Glossary
GLOSSARY
A to D Analog to Digital. Conversion of an analog signal to a digital representation.
Amplitude factor See CREST FACTOR.
Attack The rise of a musical note from zero to full volume.
Attack time The time required for an applied signal that suddenly increases in amplitude to
reach 1-(1/e), that is, 63.2% of its final, stable value.
Attenuate To reduce in amplitude.
Attenuation characteristic The decrease of signal amplitude versus frequency. It is usually expressed in
decibels per octave.
Attenuation constant See ATTENUATION CHARACTERISITIC.
Attenuator A device for reducing signal amplitude in precise, predetermined steps, or
smoothly over a continuous range.
Audibility The quality of being able to be heard. In a healthy listener, the threshold of
audibility is extremely low; at the threshold, the pressure of a sound wave
varies from normal by approximately 10
-4
pascals. The frequency range of
human audibility extends roughly from 20 Hz to 20 kHz.
Audible Hear or capable of being heard.
Boost To increase the overall level of a signal.
Clipper A circuit whose output voltage is fixed at a value for all input-voltages higher
than a predetermined value. Clippers can flat-top the positive, negative, or
both positive and negative peaks of an input voltage.
Clipping 1. Leveling off (flat-topping) a signal peak at a predetermined level. Also see
CLIPPER. 2. In audio practice, the loss of syllables or words because of
cutoff periods in the operation of the circuit (usually caused by overdriving a
stage).
Compress To reduce the bandwidth or dynamic range of a signal.
Compression 1. The reduction of output signal amplitude as input-signal amplitude rises. 2.
Processing of a signal to increase low-level components and thereby raise the
average power level. Usually a logarithmic function.
Compression ratio In a system containing compression, the ratio A
1
/A
2
, where A
1
is the gain at a
reference-signal level and A
2
is the gain at a specified higher signal level.
Compressor A circuit or device which limits the amplitude of its output signal to a
predetermined value in spite of wide variations in input signal amplitude.
Unlike a CLIPPER a compressor does not flat-top output signal peaks.
Crest factor For an AC wave, the ratio of the peak value to the rms value. The crest factor
of a sine wave is equal to the square root of 2, or 1.4142126.