Editing Dolby noise-reduction system (section)

==Dolby SR==
{{main|Dolby SR}}
The Dolby&nbsp;SR (Spectral Recording) system, introduced in 1986, was the company's second professional noise reduction system. It is a much more aggressive noise reduction approach than Dolby&nbsp;A. It attempts to maximize the recorded signal at all times using a complex series of filters that change according to the input signal. As a result, Dolby SR is much more expensive to implement than Dolby&nbsp;B or C, but Dolby&nbsp;SR is capable of providing up to 25&nbsp;dB of noise reduction in the high-frequency range. It is only found on professional recording equipment.<ref name="White1996"/><ref name="DolbySR"/>

In the motion picture industry, as far as it concerns distribution prints of movies, the Dolby&nbsp;A and SR markings refer to [[Dolby Surround]] which is not just a method of noise reduction, but more importantly encodes two additional audio channels on the standard [[optical sound]]track, giving left, center, right, and surround.

SR prints are fairly well backward compatible with old Dolby&nbsp;A equipment. The Dolby SR-D marking refers to both analog [[Dolby&nbsp;SR]] and digital [[Dolby Digital]] soundtracks on one print.