One interesting, if odd sounding, effect I found was using superstereo
on a test track for channel identity for stereo that had someone (Alan
Wiltshire) speaking from positions full left, half left, centre, half
right and full right. On my usual setting of 0.5 (range is 0 to 1.5 on
my decoder in 0.1 increments)), the speaking positions are perceived
pretty near corresponding to the left to right spacing of my front
speakers. On the 1.0 setting, the image of full left to full right is
wrapped around like a horseshoe, with left as rear left and right as
rear right with centre and 'half' positions stretched around
accordingly and somewhat broadened. But on the full 1.5 setting the
apparent speaking positions were fully reversed, with right as left
and left as right but sounding really quite focussed.
Any thoughts welcome. It darn well surprised me.
Steve
On 25 Jan 2011, at 20:53, Geoffrey Barton wrote:
On 25 Jan 2011, at 17:00, sursound-requ...@music.vt.edu wrote:
Message: 8
Date: Mon, 24 Jan 2011 12:03:11 -0700
From: Martin Leese <martin.le...@stanfordalumni.org>
Subject: Re: [Sursound] Why do you need to decode ambisonic/b format
signals ?
To: sursound@music.vt.edu
Message-ID:
<aanlktintvfioetlvgaok3gx7pbx8k0uq5opr30eyh...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Eero Aro <eero....@dlc.fi> wrote:
J?rn Nettingsmeier wrote:
in theory, you can. in practice, you can't, because you'd have to
know
what stereo technique was used during recording
Yes you can.
Just one word: Trifield.
Steven Dive <stevend...@mac.com> wrote:
...
I understand that Trifield is derived from the same groundwork as
Ambisonic, which also gives us ambi superstereo. It's a matter of
personal judgement, I think, but do you more knowledgeable theory
folks know if Trifield is therefore as flexible in its use as
superstereo?
From memory, the theory behind Trifield
assumes either Blumlein XY, or pan-potted
multi-track mono. Perhaps Geoffrey can chip
in, or somebody can look at the paper
(reference below). Again from memory,
SuperStereo assumes some sort of coincident
mic technique so, in theory, is more flexible
than Trifield. I don't know of a reference for
SuperStereo; this is a gap in Ambisonic
theory.
It is not essential that the material is Blumlein or pan potted;
that is just the way MAG handled a virtual 'test signal' in the
paper; other recording techniques work ok too, but with varying
results, much as they do over two speakers:-).
The main difference between 'Trifield' and 'Super-stereo' is that
the former works over a number of speakers >2 across the front
sector and the latter seeks to use an ambisonic array of speakers
all around the listener to lock the front in place. There were a
number of different alignments of 'Super-stereo' in various decoder
implementations, but in essence they all sought to bend the 'washing
line' of the in-phase stereo image around the front arc with
variable width, and anything substantially out of phase generally
somewhere else, again rather dependent on the source material.
Geoffrey
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