In telecommunication, the term signal compression has the following meanings:
In analog (usually audio) systems, reduction of the dynamic range of a signal by controlling it as a function of the inverse relationship of its instantaneous value relative to a specified reference level.
Signal compression is usually expressed in dB.
Instantaneous values of the input signal that are low, relative to the reference level, are increased, and those that are high are decreased.
Signal compression is usually accomplished by separate devices called "compressors." It is used for many purposes, such as (a) improving signal-to-noise ratios prior to digitizing an analog signal for transmission over a digital carrier system, (b) preventing overload of succeeding elements of a system, or (c) matching the dynamic ranges of two devices.
Signal compression (in dB) may be a linear or nonlinear function of the signal level across the frequency band of interest and may be essentially instantaneous or have fixed or variable delay times.
Signal compression always introduces distortion, which is usually not objectionable, if the compression is limited to a few dB.
The original dynamic range of a compressed signal may be restored by a circuit called an "expander".
Famous quotes containing the words signal and/or compression:
“Change begets change. Nothing propagates so fast. If a man habituated to a narrow circle of cares and pleasures, out of which he seldom travels, step beyond it, though for never so brief a space, his departure from the monotonous scene on which he has been an actor of importance would seem to be the signal for instant confusion.... The mine which Time has slowly dug beneath familiar objects is sprung in an instant; and what was rock before, becomes but sand and dust.”
—Charles Dickens (1812–1870)
“Do they [the publishers of Murphy] not understand that if the book is slightly obscure it is because it is a compression and that to compress it further can only make it more obscure?”
—Samuel Beckett (1906–1989)