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So, let me ask a question, and then conclude: Which would you rather use to compare real world performance of a speaker system *by ear*: test tones? Or you favorite CD or movie soundtrack?
I usually use music. Of the many pieces I try, one torture test is Alan Parsons' 'On Air' DTS music disc (a discrete 5.1 mix). The last track starts out with the vocalist in the left side-surround speaker speaker and walks anti-clockwise around the room, ending up in the front centre speaker. As he transitions from the left side-surround speaker to rear speaker, you can hear the hesitation in imaging; for a moment it is hard to tell if the sound is in front of you or behind. On systems where the rears are properly spread out, this problem doesn't occur.

As for the up/down vs front/back reversals; I guess we'll hear more about that when height channels gain popularity. Until then, it doesn't really matter to me if vertical reversals happen more often, because I don't have any speakers on my ceiling (though some room challenged home theatres do have in-ceiling speakers).

Speaking of ceilings... 'We Were Soldiers' was mentioned in the first post of this thread. Bit o'trivia: it is the first movie for which Dolby has encoded an overhead channel. They say it is encoded as an "extension of EX", though they haven't explained further. For home use, experts are saying that the height info may be matrixed in to the 5.1 mix or as additional data in the .1 LFE channel.
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With actual music or movie soundtracks, and with the visual cues obvious to the film format, and with *your own* head transfer function (not an average superimposed on the source signal) I still don't see where the problem comes in.
It may in fact not be a problem for you. It's entirely possible that I'm part of the population that's more sensitive to this phenomenon. Hey, I see a strobing light and want to put on some disco music; other people see a strobing light and have a seizure.
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And I suppose it does make me a little sad that a THX Ultra2 setup didn't eliminate this for Sanjay.
Yeah, those two speakers 6 inches apart basically behaved like a single sound source to my ear/brain. Ultra 2 uses some sort of Spatializer-like processing on the rears to give the impression that those speakers are further apart. I'll leave you to guess how effective it was on me.
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Got to admit, I know more now than I did before!
Glad to hear it. As you quoted one of the papers saying, "Judicious choice of room dimensions and listener location also helps to reduce front-back reversals." Reduce, not eliminate. You and Charlie may never ever experience the phenomenon during your lifetimes, but it does exist nonetheless. More importantly, several manufacturers of pre/pros, as well as several designers of surround processing, take front/back reversal into consideration. And I don't think it hurts to be aware of it.

Best,
Sanjay

[This message has been edited by sdurani (edited October 30, 2002).]
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Sanjay