When a Dolby Surround soundtrack is created in post production ( Dolby MP Matrix), four channels of sound are matrix-encoded into an ordinary stereo (two-channel) soundtrack.
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Many standalone Pro Logic decoders also included a phantom center option for compatibility with earlier non-Pro Logic Dolby Surround equipped home theaters to split the center channel signal to the L/R speakers for legacy phantom center reproduction.ĭolby Surround Pro Logic is the full name that refers to the matrix surround format and decoding system in one. It featured virtually the same type of 4 channel decoding as the Dolby Stereo theater processor with active steering logic and much better channel separation (up to 30dB) as well as including a dedicated center channel output for the first time. Later on in 1987, the Pro Logic decoding system was released to consumers. This differed from the Cinema Dolby Stereo system which used active steering and other processing to decode a center channel for dialog and center focused on screen action. The front center channel was equally split between the left and right channels for phantom center reproduction. It also had Dolby Noise Reduction and an adjustable delay for improved channel separation and to prevent dialog leaking and arriving to listeners' ears first. However, the original Dolby Surround decoders in 1982 were a simple passive matrix 3 channel decoder : L/R and Mono Surround. The same 4 channel encoded stereo track was largely left unchanged and made available to consumers as "Dolby Surround" on Home Video. This track used by the Dolby Stereo theater system on a 35mm optical stereo print and decoded back to the original 4.0 Surround.
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The Dolby MP Matrix was the professional system that encoded 4 channels of film sound into 2. It was further improved with the Dolby Pro Logic decoding system after 1987. The format was adapted for home use in 1982 as Dolby Surround when HiFi capable consumer VCRs were introduced. Dolby Surround/Dolby Pro Logic/Dolby Pro Logic II Product typeĭolby Pro Logic is a surround sound processing technology developed by Dolby Laboratories, designed to decode soundtracks encoded with Dolby Surround.ĭolby Stereo (also known as Dolby MP or Dolby SVA) was developed by Dolby in 1976 for analog cinema sound systems.