Editing Companding (section)

==How it works==
The dynamic range of a signal is compressed before [[transmission (telecommunications)|transmission]] and is expanded to the original value at the receiver. The electronic circuit that does this is called a compander and works by compressing or expanding the [[dynamic range]] of an analog electronic signal such as sound recorded by a microphone. One variety is a triplet of amplifiers: a [[logarithmic amplifier]], followed by a variable-gain linear amplifier, and ending with an exponential amplifier. Such a triplet has the property that its output voltage is proportional to the input voltage raised to an adjustable [[Exponentiation|power]].

Companded quantization is the combination of three functional building blocks – namely, a (continuous-domain) signal dynamic range ''compressor'', a limited-range uniform quantizer, and a (continuous-domain) signal dynamic range ''expander'' that inverts the compressor function. This type of quantization is frequently used in telephony systems.<ref name=Bennett>W. R. Bennett, "[http://www.alcatel-lucent.com/bstj/vol27-1948/articles/bstj27-3-446.pdf Spectra of Quantized Signals]", ''[[Bell System Technical Journal]]'', Vol. 27, pp. 446–472, July 1948.</ref><ref name=GrayNeuhoff>[[Robert M. Gray]] and David L. Neuhoff, "Quantization", ''[[IEEE Transactions on Information Theory]]'', Vol. IT-44, No. 6, pp. 2325–2383, Oct. 1998. {{doi|10.1109/18.720541}}</ref>

In practice, companders are designed to operate according to relatively simple dynamic range compressor functions that are suitable for implementation as simple analog electronic circuits. The two most popular compander functions used for telecommunications are the [[A-law]] and [[μ-law]] functions.