Hi,
I'm curious as to where "normal" stereo at plus and minus 30 degrees
comes from.
Most "stereo" microphones use two cardioid capsules at 90 degrees
(plus and minus 45 degrees) or wider. MS and ambisonics derive from
Blumlein, the first using a central cardioid with a figure-8 at right
angles to it, and the latter with an omni-directional pressure
microphone and figure-8 microphones at 90 degree separation. Most
mono panpots use a sin/cosine law based on 0 to 90 degrees. The only
argument for plus and minus 30 degrees I've heard was based on a
potential "hole in the middle", that I have never really encountered,
and screen-based media which favour a narrow audio image to match the
narrow visual image. 5.1 seems to have legitimised the zero, plus and
minus 30 degrees, and plus and minus 110 degrees (more side than
rear) heresy.
Even our own ears are not at plus and minus 30 degrees, more like
plus and minus 75 degrees or larger separation.
Others, including I think Robert Green, have argued for 90 degrees
instead of 60 degrees.
"Normal" stereo via UHJ to B-format, does reveal spatial information
beyond left and right in stereo recordings. Spaced omni recordings,
of course, have no definite spatial directionality.
Ciao,
Dave Hunt
From: Eero Aro <eero....@dlc.fi>
Date: 26 March 2016 12:36:42 GMT
To: sursound@music.vt.edu
Subject: Re: [Sursound] Static stereo source in rotating
soundfield, possible?
Reply-To: eero....@dlc.fi
Hi
When you use two channel stereo in the 360 soundfield, pay
attention to two
things.
If you pan the Left and the Right channel of the stereo into
directly opposite directions,
say + 90 and - 90 degrees (to left and right), you basicly lose the
directional cues.
What you hear is a very spacious sound image. You cannot detect the
directions of individual phantom sources. If this is what you need,
do it. It's about
the same which directions you use, as rotating the opposite panned
stereo doesn't
change the illusion practically at all. This technique has been
used with dummy head
recordings, and yes, it is spacey, but no good sense of directions.
If you wish that a stereo image is located somewhere around you, it
is better to pan the
Left and the Right channel to some certain angle from each other.
Try first
panning the stereo channels to + 30 and - 30 degrees in front, as
in a normal two
loudspeaker stereo. You will notice that it sounds a little bit
like two channel stereo,
but with worse localization, at least in first order Ambisonics.
You can then rotate this
"sector" to some other direction. At the back and at the sides the
localization is
not as good as in the front, and it is usually better to narrow
down the sector.
This is not because of Ambisonics, it's because our hearing
localizes phantom sources
from loudspeaker playback in that way.
I have used this technique in "smearing" the localization of a
panned mono signal.
The mono is panned into some direction and the stereo reverb or
delays of that
mono signal panned into both sides of the mono image.
if this is the equivalent of fitting a square peg into a round
hole...
Or "drilling a square hole with a triangular drill"? :-)
Not at all. I think your question is very relevant and welcomed. I
wish there would
be more discussion about how the soundfield is used in real life.
Eero
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