Science Fair Project Encyclopedia
In telecommunication, signal processing, and thermodynamics, companding (occasionally called compansion) is a method of reducing the effects of a channel with limited dynamic range. It is a combination of compressing and expanding, and is a variant of audio level compression.
While the compression used in audio recording and the like depends on a variable gain amplifier, and so is a locally linear process (linear for short regions, but not globally), companding is non-linear and takes place in the same way at all points in time. The dynamic range of a signal is compressed before transmission and is expanded to the original value at the receiver.
The use of companding allows signals with a large dynamic range to be transmitted over facilities that have a smaller dynamic range capability. Companding reduces the noise and crosstalk levels at the receiver.
This is sometimes used in digital systems, compressing before input to a analog-to-digital converter, and then expanding after a digital-to-analog converter. This is equivalent to using a non-linear ADC. This is also used in digital file formats for better signal-to-noise ratio at lower bit rates. For example, a linearly encoded 16-bit PCM signal can be converted to an 8-bit WAV or AU file while maintaining a decent signal-to-noise ratio by compressing before the transition to 8-bit and expanding after a conversion back to 16-bit. This is effectively a form of lossy audio data compression.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details