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 (the word companding therefore is a portmanteau word), and is a variant of audio level compression. BlackBerry 7100t Telecommunication refers to communication over long distances. ... Signal processing is the processing, amplification and interpretation of signals. ... Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics that studies the effects of temperature, pressure, and volume changes on physical systems at the macroscopic scale. ... Dynamic range is a term used frequently in numerous fields to describe the ratio between the smallest and largest possible values of a changeable quantity. ... Look up Portmanteau in Wiktionary, the free dictionary. ... Audio level compression, also called compression or limiting, is a process that manipulates the dynamic range of an audio signal. ...

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. In communications, transmission is the act of transmitting electrical messages (and the associated phenonomena of radiant energy that pass through media). ...

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. In science, and especially in physics and telecommunication, noise is fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector. ... In telecommunication, the term crosstalk (XT) has the following meanings: 1. ...

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. In electronics, an analog-to-digital converter (abbreviated ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers. ... In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or charges). ... PCM is an initialism which can have different meanings: Phase Change Material Pulse-code modulation, a way to digitally encode signals representing sound and their video counterparts Potential Cancer Marker Communist Party of Mexico Plug Compatible Manufacturer Power-train control module, a computer in a car which controls the car... WAV (or WAVE), short for WAVE form audio format, is a Microsoft and IBM audio file format standard for storing audio on PCs. ... The Au file format is a simple audio file format that consists of a header of 6 32-bit words and then the data. ... Note: This article is about audio data compression, which reduces the data rate of digital audio signals. ...

See also

• Dolby system
• mu-law
• A-law

The Dolby logo Dolby Laboratories, Incorporated (Dolby Labs) (NYSE: DLB) is a company specializing in audio compression and reproduction. ... In telecommunication, a mu-law algorithm (μ-law) is a standard analog signal compression or companding algorithm, used in digital communications systems of the North American and Japanese digital hierarchies, to optimize (in other words, modify) the dynamic range of an audio analog signal prior to digitizing. ... An a-law algorithm is a standard companding algorithm, used in European digital communications systems to optimize, modify, the dynamic range of an analog signal for digitizing. ...

External links

• A description of companding in wireless microphones