Didn't Lauridsen propose and experiment with
stereo playback done this way--with a mono signal
in the center and a diffference signal produced by a edgeon mounted
dipole?
Robert
On Wed, 22 May 2013, J?rn Nettingsmeier wrote:
Hi Ray,
On 05/22/2013 01:24 AM, revery wrote:
Hello j?rn,
Thinking about what you say here, is this working by having pure M
from the front and S from 90 degrees to the side, effectively
'mixing' the M S signals in the air as they reach the ears/brain?
(Maybe I'm thinking about this too much, my brain is hurting.)
Maybe :)
Think about it this way: MS is a subset of Ambisonics, effectively missing
the front-back and up-down information. So we can use it as an Ambi mic:
The Mid signal gets panned where I need it. The Side signal is then used to
give it a bit of width. For a frontal source, it will be fed to the Y channel
only. Note there is no pressure component W from this signal.
The only slight complication is that your side signal is not coincident with
the main microphone, so you have to watch out for your overall image.
If so,
is there significant distortion/corruption of the effect from the two
ears receiving different variations of the M and S signals?
There is no coloration other than what's inherent in Ambisonics.
I realise
that ear crosstalk effect is an issue with standard two speaker
stereo as well, but the consequences with this kind of signal
presentation seem to me to be quite different. As part of this, if
the head turns say 45 degrees to the left, the ear difference would
seem to be at a maximum, with the left ear receiving a significant
amount of the opposite lobe of the figure 8 with little cancellation
effect from the M in front. Perhaps this is all part of the plan?.?
Like I said, there is no magic mixing in the air.
Ear crosstalk is not an issue in Ambisonics - we try to recreate a sound
field, and the head is in there like it would be in the original field at the
concert. So "ear crosstalk" is very much part of the experience.
What you will hear is pretty much a widened version of the M signal. It's not
strictly orthodox, but it works, as long as you don't overdo it and you get
your delays right.
For a less confusing way of mixing MS spots into Ambisonics, you can render
them to Left-Spot and Right-Spot with a conventional MS matrix, and then pan
those individually. Because they are coincident, there will be no comb filter
artefacts, no matter how close you pan them.
The reason I treat the S signal separately is because I usually work in third
order, so the M mic is pretty sharp, and the S mic is then fed to first order
only.
The problem with this kind of mixed-order hackery is that the sound might
shift when you truncate orders on playback (if no 3rd order system is
available), but I already have this problem: my main mic is a first-order
tetrahedron anyways. So I just watch out for it while mixing and frequently
cross-check at lower orders to arrive at a useful middle ground.
Best,
J?rn
--
J?rn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister f?r Veranstaltungstechnik (B?hne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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