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Dolby Pro Logic II

A much improved decoding system for Dolby Stereo encoded material and also caters to the decoding of non-encoded material such as regular two channel music. It differs from it predecessor by achieving a more intelligent extraction of the channels, so much so that instead of a single surround signal, Dolby Pro Logic II yields stereo left and right surrounds. For compatibility with movies and other Dolby Stereo encoded material, Pro Logic II has a Movie mode. Because non-encoded material such a music more often than not collapses to center (all the sound seems to come just from the center speaker), Pro Logic II also has a Music mode which works extremely well and can include user access to parameters to customize the sound field.

Surround EX
Dolby Digital Surround EX first appeared in movie theaters with Star Wars Episode I: The Phantom Menace. This system starts from a standard Dolby Digital 5.1 soundtrack but then applies a form of Pro Logic decoding to the two rear channels only, and derives a third surround channel, positioned between the other two. So from a 5.1 soundtrack, Dolby Digital Surround EX derives a 6.1 soundtrack.

This new system first became available to the home market on THX equipment as THX Surround EX because THX co-created the new system. It is now available on non-THX decoders as Dolby Digital EX. Ideally, a soundtrack needs to have been crafted for this system in order for it to sound right. The surround sound information of non-EX encoded tracks can come out predominantly from the center surround channel and lose spaciousness.

DTS ES and ES Discrete
DTS also delivered some 6.1 systems. The first, DTS ES, is in all practicality the same process as Dolby Digital EX in that the playback system applies a matrix decoder to the two surround channels to derive a third between them. DTS ES Discrete on the other hand actually added a sixth discrete main channel. Where as there are precious few Dolby Surround EX soundtracks on DVD, there are even fewer DTS ES and fewer still DTS ES Discrete. That sixth channel has just not been very successful.

Dolby Pro Logic IIx
Dolby Pro Logic IIx takes virtually any source track, be it two channel or 5.1, and yields up to seven channels of sound by employing the latest in matrix decoding technology.