CV cluster as MS decoder
2004-07-12 by Fernando
Hi Ken and all,
Reading again the CV-cluster page I realized that it can be used as an MS decoding matrix
when feeded with audio signals.
Decoding an MS (read Mid Side stereo) signal will result in the Left and Right channels if
the origin was a pair of mics setup for that kind of stereo recording (usually a cardioid for
M and a figure-of-8 for S) but it can impart very special, weird, interesting spatial
characteristics to signals not originally intended for MS decoding, as you mention there,
btw:
Reading again the CV-cluster page I realized that it can be used as an MS decoding matrix
when feeded with audio signals.
Decoding an MS (read Mid Side stereo) signal will result in the Left and Right channels if
the origin was a pair of mics setup for that kind of stereo recording (usually a cardioid for
M and a figure-of-8 for S) but it can impart very special, weird, interesting spatial
characteristics to signals not originally intended for MS decoding, as you mention there,
btw:
Show quoted textHide quoted text
>It of course can be used with audio frequency signals too, and may proveSo, here we have an stereophonic special effects unit out of the CV-cluster.
>interesting when driving a cluster of wave multipliers or similar. Two audio signals
>fed to it could produce interesting stereo effects.
Once more, it's amazing how versatile the CGS modules are! Million thanks again, Ken!
Fernando
P.S. About MS stereo: An old technique used very often nowadays to record sound in
documentaries and feature films (and in the studio also). Very commonly used by the BBC
for many years. Please make a search ("mid side stereo") to learn about it instead of
reading my unacurate explanation!
The mics are placed as a coincident pair (= with the diafragms very close together, as if
they were in the same point in the space, to avoid phase differences = the mics are at the
same distance from the "sound subject").
The cardioid (that can be an hypercardioid or an omni too) is facing the sound source
(front) and the fig.8 is facing the sides (hence the name Mid Side stereo, or MS stereo)
The fig.8 mic is a special mic with a polarized diafragm, similar to two cardioid mics facing
oposite sides, but using a single -polarized- diafragm. Since it's polarized, sound coming
from one side (L) results in positive signal and sound coming from the other (R), negative.
We record the front mic M in one channel (1) and the S mic in another channel (2).
The decoding procedure is very simple: the resulting Left channel is M plus S, and the
resulting Right channel is M minus S (= M+(-S), were S is phase-inverted).
So, sum and difference. That is why I realized the CV cluster could be used as an MS stereo
decoding matrix, comonly known as "MS matrix"
One interesting fact (that we can use here) of the MS technique is that by varying the ratio
of the M and S signals while decoding, you make the resulting stereo signal more or less
"wide". A ratio of 50:50 gives a balanced front and sides image; 70:30 has more center
and less sides, 30:70 more sides than center, etc.
So adding complementary VCAs at the input of the cluster can be interesting too.
Anyhow, when you "decode" sounds that are not actually in MS the results are quite
interesting! More if you play with the phase, sign and amplitude of the signals you send to
the matrix.
Have fun!