Re: Outputting Multichannel sound from stereo sources
Re: Outputting Multichannel sound from stereo sources
- Subject: Re: Outputting Multichannel sound from stereo sources
- From: Richard Dobson <email@hidden>
- Date: Thu, 12 Aug 2010 20:56:58 +0100
Probably meant for the list.
-------- Original Message --------
Subject: Re: Outputting Multichannel sound from stereo sources
Date: Thu, 12 Aug 2010 19:03:09 +0100
From: Dave Hunt <email@hidden>
To: email@hidden
Hi,
On 12 Aug 2010, at 16:04, Richard Dobson wrote:
On 12/08/2010 15:28, Simon Thorpe wrote:
Paul,
..
So, if anyone can point to me to a place that can sell me
multichannel
recordings, I'd be grateful. But, in the meantime, I would just
like to be
able to play music through more than 2 speakers. Surely, this is
not so
unreasonable?
But - it may not be quite as "reasonable" an idea as you may think.
What, ~exactly~, do you want/expect to come out of the extra
channels? Most people use surround to enhance auditory
localization, and/or the sense of "being there" - hence the use of
the surround channels to project the reverb one would hear from
behind (and to the side etc) in a live performance presented from a
front stage; in principle, to capture and reproduce the full
"soundfield" in Ambisonic parlance. If you want somehow to hear the
music sort-of remixed with different instruments routed to
different channels, you will be pretty much out of luck. There are
techniques for demixing ("blind source separation" etc), but they
are both complex and limited.
MPEG surround is attempting to do this by compressing multi-channel
sound to stereo, along with de-multiplexing data, and it does sort of
work. Who knows whether it will ever become widely used or available.
Unless really done carefully, more speakers = worse sound, not
better. Shock and awe maybe; but not quality, clarity or
refinement. You might like to consider the notion that using more
speakers simply because they are there may not in fact give you the
results you suppose. You can be confident that good stereo is far
better than bad surround!
The likelihood is, after the thrill of the novelty has subsided,
that you might actually find (especially if you set up your stereo
speakers really carefully, which most people do not bother to do)
that good old stereo both sounds really good and can be
surprisingly enveloping. None of the 5.1 and 7.1 layouts is
optimally suited to good soundfield reproduction, as those layouts
are so geometrically irregular. Conversely, a precisely laid out
plain rectangular quad layout (hence, front pair at +- 45degrees)
can sound surprisingly good. Better then to reserve your surround
speakers for music expressly recorded that way in the first place.
Which inter alia takes you back to Ambisonics and the above site.
Passing stereo through a UHJ Ambisonic decoder is as, if not more,
effective than Dolby Prologic stereo algorithms. Crossed pair
microphone, or even studio pan-potted recordings work better than
spaced omni mic recordings. I've built similar things in Max/MSP, and
it's not particularly difficult. If you do UHJ to B-format, you can
then make all sorts of adjustments to the spatiality in B-format
before decoding to the speakers.
You can always move 5.1 speaker layouts around so that you have more
of a pentagon than an irregular layout. True Blumlein stereo should
have left and right speakers at plus and minus 45 degrees from centre
anyway. 5.1 came from cinema with a fairly narrow front image, and a
diffuse rear splodge.
NB this is not really directly pertinent to CoreAudio development,
so is probably OT for this list.
I'm not so sure. There are odd references to ambisonics in Core
Audio, and a resurgence of interest in it generally. If we can
encourage the development of a better and more flexible surround
sound architecture in things like Logic, then such experiments in
surround will become within everyone's reach, and surround sound will
improve. Reaper, Cubase and Max seem to manage it, though you have to
search for the tools, or build them yourself.
Ciao,
Dave
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