Surround Sound Primer

Secrets of Home Theater and High Fidelty has an updated article on Surround Sound Processors and Receivers that covers all of the basics of surround sound system. They cover the history of surround sound and the many ,many different formats available today such as Dolby Pro Logic, Dolby Digital, and so forth.

Dolby Pro Logic, like Dolby Stereo in the movie theater, converts two tracks of sound into four channels.

Dolby Digital (also known as the AC-3 Codec) was first made available to consumers on special Laserdiscs.  It came into the mainstream when it was chosen as the multi-channel codec for the DVD Video format.  It is an extremely flexible codec which can carry from 1 to 6 completely separate and independent channels of digital sound.  The full six-channel configuration consists of the front left, center, front right, rear left and right, and the LFE channel (or Low Frequency Effects channel). The LFE channel has a restricted frequency range, while all the other channels are full range (8 Hz - 20 kHz), so the system is often called "5.1".

Digital Theater Systems, or DTS, is another 5.1 digital surround sound format, first developed for movie theaters and then later appearing in homes on Laserdiscs.  It is now technically an optional format for DVD.  The system utilizes a completely different lossy compression codec from AC-3, and only manages a 5:1 compression. …  There are some who feel that the DTS codec results in better sound because it uses less compression, but because the two codecs are different, the bitrates cannot be compared at face value (i.e.,  it could simply be that DTS is less efficient than AC-3 as opposed to actually sounding better).  We at Secrets have never been able to definitively show that DTS sounds any better than Dolby Digital.

Dolby Pro Logic II is 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.

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.

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.

This is really a great read if you are building a home theater system. Dolby Digital is probably the most known surround sound format introducing the 5.1 speaker system (front left, front right, center, rear left, rear right).

Here’s an excellent description of 5.1 surround sound:

True surround sound formats rely on dedicated speakers that literally and physically surround the audience.  There is one center speaker which carries most of the dialog (since the actors usually speak while making their on-screen appearance), and part of the soundtrack.  There are left and right front speakers that carry most of the soundtrack (music and sound effects), and may carry parts of the dialog (when the director wants to intentionally off-set the source of the dialog to either side, from its default dead-center screen location).  There is a pair of surround sound speakers that is placed to the side (and slightly above) of the audience to provide the surround sound and ambient effects.  Finally, a subwoofer can be used to reproduce the low and very low frequency effects (LFE) that come with certain movies (e.g., the foot-stomping bass effects in "Jurassic Park" and "Godzilla").

So what surround sound format is the best for a home theater PC, considering most of your video is coming from a DVD? Does anyone recommend anything other than Dolby Digital 5.1?