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Surround Sound Expansion The best of the older matrixed Dolby decoders is Dolby Pro Logic - which expands a two-channel stereo sound track to four channels played over five speakers, front left and right, front center, and two speakers for a mono surround, plus an optional sub-woofer. Sound from a Dolby Pro Logic decoder for surround-encoded movies sounds good, but it has little detail in the surround as a result of its single, frequency-limited (cut-off at 7kHz) monaural surround signal. Further more, while a Dolby surround sound Pro Logic decoder can be driven by any stereo sound track, yet CDs and other stereo music content does not really sound like surround. This Pro Logic decoder tends to throw too much of the mix into the front center speaker when driven by ordinary stereo content - thus resulting in an unbalanced surround sound field. In other words, you cannot just leave the Pro Logic mode 'on' at all times. This deficiency eventually led to the design of a second matrixed-decoder, Dolby Pro Logic II, in an attempt to achieve a cleaner sound that meshes better with any stereo content.
But there are further differences from the original Pro Logic Dolby surround sound process. Dolby Pro Logic II transforms any stereo signal into five-channel, full-bandwidth surround sound in contrast to the 7 kHz frequency-limited monaural surround of the former. This yields a better surround sound-stage that is ideally suited for home theater systems. Dolby Pro Logic II also provides more control of the center image and front/rear balance. And it does all this with a simpler processing, thus yielding even cleaner sound. Finally, it is designed for use with both surround-encoded sources as well as with any ordinary stereo sound track. This means that it can provide an expansive surround sound-stage even for ordinary stereo content.
It is found in the Apple®
iPod®, in MP3 and CD playback, in VHS movies, in laser
discs, and in stereo broadcasts.
Pro Logic II decoders support three listening modes, with the most important being 'music' and 'movie'. Thus, in the music mode, it provides a more spacious feel than in the dialogue oriented movie mode. Further more, its 'dimensional control' provides the user with a sort of front/rear balance control that may turn out useful for certain content, e.g. if your stereo content provides little room ambience, you can literally break up the front focused soundstage to let it breathe towards the rear. As with all multi-channel audio playback systems, Pro LogicII Dolby surround sound systems require precise speaker placement to produce the best enveloping soundstage. For speaker placement details associated with multi-channel surround sound, please refer to our Home Theater Speaker Placement article.
The actual number of playback channels dependents on your speaker playback setup rather than the Pro Logic IIx technology itself. This technology is featured in iPods, MP3 and CD playback, DVD-Video, VHS movies, laser discs, and in stereo and surround broadcasts.
With Pro Logic IIx, any
movie, CD, TV program or video game can be enjoyed through this
enhanced Dolby surround sound technology, thus creating a seamless,
natural surround soundfield that immerses you in the
entertainment experience.
Next: Dolby Virtual Surround Sound ...back to Dolby Sound Formats Sec. Index
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Speaker Placement in Multi-Channel Audio Correct home theater speaker placement plays a critical role towards achieving that seamless ‘enveloping’ sound so important in the overall home theater experience.
Time Delay
Settings in Surround Sound Systems
THX Home
Cinema - An Overview
Selecting and Installing Speaker Wire To access the full range of home theater design guides appearing on our site, click here.
Books & Magazines
Home Theater
Practical Home Theater A well written reference guide to home theater.
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