[Scott Dorsey]

William Sommerwerck wrote:
Briefly, Gary...

The idea that the room should interact with the playback was pretty much
abandoned with the introduction of consumer stereo playback. (I'm not sure it
was ever taken seriously even in the days of mono.) It is a fundamentally
impractical idea, because you are stuck with whatever room you have. And even
assuming an "ideal" image projector could be built, it would be horribly
expensive, as it would require far more high-quality drivers than a
conventional speaker system.

The thing is, you _can't_ totally eliminate room effects. It would be nice
if you could, but you can't.

So, you're stuck with some room effects, and if properly done those room
effects can be used to improve stereo imaging. The whole LEDE thing is
a very good example of how an improved sense of space can result from
playback room reflections.

But... the room reflections should never be dominant and should never
overpower the ambience present in the original recording.

And no... you _aren't_ stuck with whatever room you have. If you want
an accurate playback system, the room needs to be designed with controlled
acoustics and the speaker system needs to be designed into the room.

But total elimination of room effects is possible to do, and if you ever
listen to playback in an anechoic chamber it is quite interesting but
not necessarily accurate or useful.

As for "decoding" the ambience in the recording... This has been known for
decades. The brain doesn't do a good job of localizing uncorrelated sounds. If
the program is delayed about 15ms and played through speakers to the sides,
the random-phase ambient components become sufficiently decorrelated that they
are heard as an enveloping ambience. The direct sounds are not random-phase,
and are still within the fusion region, so they still appear to come from the
front.

I'll point out that the inability to corellate position of sounds widely
separated in time is ALSO what makes widely spaced omni recordings work. The
brain is unable to make anything of the phase differences and so all the
imaging is the result only of intensity differences.

It's unfortunate you're wasting so much time and money on what appears to be
absolutely useless research, when you could be having a lot more fun listening
to a properly configured surround system. When I play a surround SACD, or use
a hall synthesizer, I get little, if any, sense that I'm hearing the ambient
acoustics of my (untreated) room.

Many of these systems work well when your head is pointed forward, but
come apart when you turn your head to the side. Admittedly, that does
not seem too severe a drawback, especially for sound-for-film.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."