Dolby Laboratories’ original motion picture film soundtrack system that encodes four channels of sound (left, center, right and surround) into a two channel photographic sound track, incorporating Dolby A-type noise reduction and extended frequency response. 1 These are then printed on the film.
Dolby playback equipment is used to convert the two tracks on the film back into four channels of sound in the cinema.
Dolby SR (spectral recording) A powerful analogue Dolby system used for the analogue soundtracks on all Dolby Digital prints and on many analog only releases.
Dolby SR*D This term is used by the film industry to identify 35mm release prints containing both an analogue Dolby Stereo SR (‘SR’) and Dolby Digital (‘D’) optical soundtracks (square blocks of data located between the sprockets).
Dolby Surround, Dolby Stereo, Dolby 4:2:4 Matrix: Analogue coding of four audio channels – Left, Centre, Right, Surround (LCRS), into two channels referred to as Right-total and Left-total (Rt, Lt). On playback, a Dolby Surround Pro Logic Decoder converts the two channels to LCRS and, optionally, a sub-woofer channel. The Pro Logic circuits are used to steer the audio and increase channel separation. The Dolby Surround system, originally developed for the cinema, is a method of getting more audio channels but suffers from poor channel separation, a mono limited bandwidth surround channel and other limitations.
A Dolby surround track can be carried by analogue audio or linear PCM, Dolby Digital and MPEG compression systems.
1 Case, D., 1985, Motion Picture Film Processing, Media Manuals, Focal Press, London, Boston