Dolby Pro Logic and Dolby Surround are both playback technologies, with the movie itself being in analog Dolby Stereo. Pro Logic uses an active matrix, while Dolby Surround uses a passive matrix. That means Pro Logic uses steering logic, while Dolby Surround subtracts right channel from left channel and puts the difference in the back, with time delay. Dolby Surround has very little separation, and is antiquated at this point. Actually, Pro Logic 2 makes Pro Logic antiquated, too, with faster steering logic, full-range stereo rears, and a startling absence of audible artifacts. The attack and release times of the control voltages in the Pro Logic matrix are very slow, in order to be smooth to compensate for flawed software of the mid-80s.
Dolby Stereo, the precursor to Dolby Digital, incorporated Dolby B-type noise reduction and Dolby Surround encoding. When you see a film with a Dolby Stereo logo in the credits it means it has been surround encoded along with Dolby noise reduction appropriate for motion picture applications.
When you see a television program, such as The Sopranos, with the Dolby Surround logo in the credits this simply means the soundtrack has been surround-encoded in a manner appropriate for television broadcast or video playback.
A Dolby Surround processor (passive, no steering) or a Pro Logic processor (with steering) will decode a Dolby Surround-encoded or Dolby Stereo soundtrack delivering a mono surround track.
A Pro Logic II equipped processor will decode the soundtrack delivering a more exciting stereo surround listening experience comparable to a DD 5.1 playback.
Originally posted by Mr. Hookup There is another difference: Dolby Surround is the older system that has no center channel speaker level output; Dolby ProLogic does have chenter channel speaker level outs.
Iv read this on a few websites too. But this is what confuses me on Dolby Sourround VHS movies I get sound from all 6 channels.
Dolby Surround when passively decoded provides Lf, Rf and mono surround or three channels plus a fourth phantom center. Dolby Surround when decoded with a Pro Logic (active/steered) processor provides the additional center channel output.
There is output from Pro Logic decoders on both the left and right surround channels but it is essentially identical signal information.
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