Surround...

Somebody's gotta kick off the interactive offer on your new site [congratulations by the way] so here's a question for you. In a live acoustic music environment, direct sound reaches the listener only from the stage front. During playback, the listening room characteristics impose their own reflections and artificial ambience that cannot be the same as that of the original venue. Music surround sound pundits claim that the surround speakers can recreate the original ambient cues better than traditional stereo. This is different from bombarding the listener with "main" information from all sides which is obviously artificial since no direct sound reaches a listener from behind in a live environment.

How is the ambient information extracted from two-channel music sources, to be routed to the surround channels in a music surround sound format?

...Srajan Ebaen
SoundStage! columnist and die-hard two-channel dinosaur

In a music context, you're right that the direct sound is almost always up front and that the material coming from other directions constitutes reflections. Very few of the rooms we listen in are large enough to simulate the ambience of a concert hall, so two-channel listening at home is frequently very different from a live experience. It comes closer when the ambience of the larger space is included in the recording and reproduced by its own dedicated speakers. Ideally, this is done intentionally at the mixing stage, but even with recordings not specifically encoded for surround, very realistic effects can be obtained by using a Pro Logic decoder. Much of the ambience is out of phase with the main signal, and it is this out-of-phase material that is fed to the surround channels.

Bombarding the listener with "main" information from all sides, as you put it, is often desirable with movie sound.

...Ian G. Masters