The Dolby SR (Spectral Recording) noise reduction format was developed by

Dolby Laboratories Dolby Laboratories, Inc. (often shortened to Dolby Labs and known simply as Dolby) is an American company specializing in audio noise reduction, audio encoding/compression, spatial audio, and HDR imaging. Dolby licenses its technologies to ...

and has been in common use in professional audio since 1986 and in cinema audio since the late 1980s. It is a revised version of Dolby's earlier formats, combining aspects of Dolby A, B and C (e.g., sliding band and fixed band

compander In telecommunication and signal processing, companding (occasionally called compansion) is a method of mitigating the detrimental effects of a channel with limited dynamic range. The name is a portmanteau of the words compressing and expanding, ...

s) to improve the

dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base ...

(i.e., the range in decibels between peak level and noise floor) of analogue recordings and transmissions by as much as 25 dB. Dolby SR is used in many modern professional audio analogue (i.e., tape) recordings by recording and

postproduction Post-production is part of the process of filmmaking, video production, audio production, and photography. Post-production includes all stages of production occurring after principal photography or recording individual program segments. Th ...

engineers, broadcasters, and other audio professionals. It is used as the optical analog format on almost all 35mm film release prints, and is always the accompanying optical analog format when Dolby Digital is present. Dolby SR was originally implemented in Dolby's Cat. 280 card, which was pin-compatible with the Cat. 22 A-type noise reduction card. Thus, devices that took the Cat. 22 card could be upgraded from A to SR by replacing the Cat. 22 with the Cat. 280. The Cat. 280 card functions in many devices including Dolby's Model 361 frame. Some Dolby Cinema processors require a special version, the Cat. 280T, which functions for decoding (playback) only.

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