by radio transmission. Companding also reduces the noise and crosstalk levels at the receiver. Companders are used in concert audio systems and in some noise reduction schemes. History The use of companding in an analog picture transmission system was patented by A. B. Clark of AT&T in 1928 (filed in 1925): In 1942, Clark and his team completed the SIGSALY secure voice transmission system that included the first use of companding in a PCM (digital) system. In 1953, B. Smith showed that a nonlinear DAC could be complemented by the inverse nonlinearity in a successive-approximation ADC configuration, simplifying the design of digital companding systems. In 1970, H. Kaneko developed the uniform description of segment (piecewise linear) companding laws that had by then been adopted in digital telephony. In the 1980s (and '90s), many of the music equipment manufacturers (Roland, Yamaha, Korg) used companding when compressing the library waveform data in their digital synthesizers. Unfortunately exact algorithms are not known, neither if any of the manufacturers ever used the Companding scheme which is described in this article. The only known thing is that manufacturers did use data compression in the mentioned time period and that some people refer to it as "companding" while in reality it might mean something else, for example data compression and expansion. This dates back to the late '80s when memory chips were often one of the most costly components in the instrument. Manufacturers usually quoted the amount of memory in its compressed form: i.e. 24 MB of physical waveform ROM in a Korg Trinity is actually 48 MB when uncompressed. Similarly, Roland SR-JV expansion boards were usually advertised as 8 MB boards with '16 MB-equivalent content'. Careless copying of this technical information, omitting the "equivalence" reference, can often cause confusion. References External links Companding: Logarithmic Laws, Implementation, and Consequences Lossy compression algorithms Audio engineering Sound recording technology