M-S Recording

 

Most of us may have wondered what the secret is behind the fat stereo grand piano sound so frequently heard on the Blue Note albums of the 50s and early 60s... well, the answer is the M-S miking technique.

M-S is a nifty mike setup that produces amplitude stereo only, in a most sophisticated way. You use two coincidential large-diaphragm condenser mics for the piano, one set to cardioid, the other to figure-8. Adjust the cardioid to point toward the strings, and the figure-8 perpendicular to that. If you want to record some room resonance, it is advisable to use spheroid instead of cardioid. What you'll get in the output is the pure mono signal on the cardioid/spherical channel, and the difference of the L and R channels on the figure-8 (keep in mind that either side of the figure-8 is phase-reversed to the other).

So, how do we mix that? We need three mixer channels for our two mikes; one for the cardioid/spherical, the other two for the figure-8. What you do is you run the figure-8 into both mixer channels, and hit phase reverse on one of these. Pan them hard left and right. Now, by adjusting the three faders combined, we can set the absolute volume, while moving the figure-8 faders with respect to the cardioid fader boosts/cuts the stereo effect.

The nice thing about this technique is that you get a fully-adjustable amplitude stereo only; no time-offset stereo involved there with all its drawbacks like comb filtering and mono incompatibility. Plus the sound is so nice and warm... I frequently use this setup for live recording too.

An interesting offshoot of this technique is that you can use it also in reverse; that is, make an M-S signal from a standard LR stereo source. It works like this: The M channel is the average over the L and R channels; the S channel is their difference. From the resulting M-S file, you can compose stereo again by adding a variable amount of S or -S to the M channel, thereby influencing the stereo "spread". This is tremendously helpful like when notating music from a recording, as you can focus on a single instrument better if the stereo spread is fairly wide. On the other hand, you can make older recordings with "hard stereo" (some early Hendrix comes to mind) more pleasurable to listen to by cutting its stereo component.

When used in conjunction with a scaling factor, the transformation between L-R and M-S stereo is exactly symmetrical:

is exactly equal to:

Below, you can find a perl listing that can do the conversion for you. It requires perl and SoX (Sound EXchange) installed.

Caution: This code is untested. Nevertheless, have fun!

#!/usr/bin/perl
use warnings;
use strict;

###########################################
# ms2stereo
# A Program to Generate LR stereo from M-S
# and vice versa
# (c) Amelie Zapf 2005
# Licensed under the GNU GPL Version 2
# Usage: ms2stereo <amount> <infile> <outfile>
# <amount> is a floating-point number
# <amount> must be 1.0 for LR->MS
###########################################

my ($samount, $infile, $outfile)=@ARGV;

my $fileroot=$infile;
$fileroot=~s/\.[\w\d]+$//;

my $factor=2**(-0.5);
my $sfactor=$factor*$samount;

print "Splitting channel 1 and Attenuating...\n";
`sox $infile -c 1 $fileroot.1.wav avg -l vol $factor`;
print "Splitting channel 2 and Attenuating...\n";
`sox $infile -c 1 $fileroot.2.wav avg -r vol $sfactor`;
print "Creating new channel 1...\n";
`soxmix $fileroot.1.wav $fileroot.2.wav $fileroot.new1.wav`;
print "Inverting channel 2...\n";
`sox $fileroot.2.wav $fileroot.2inv.wav vol -1.0`;
`rm $fileroot.2.wav`;
print "Creating new channel 2...\n";
`soxmix $fileroot.1.wav $fileroot.2inv.wav $fileroot.new2.wav`;
`rm $fileroot.1.wav`;
print "Creating mergeable stereo...\n";
`sox $fileroot.new1.wav -c 2 $fileroot.sleft.wav pan -1.0`;
`sox $fileroot.new2.wav -c 2 $fileroot.sright.wav pan 1.0`;
`rm $fileroot.new1.wav $fileroot.new2.wav`;
print "Merging...\n";
`soxmix $fileroot.sleft.wav $fileroot.sright.wav $outfile`;
`rm $fileroot.sleft.wav $fileroot.sright.wav`;
print "Done. Your stereo output is in $outfile.\n\n";

 

Writings

Diese Seite gibt's leider nur auf Englisch!

On Music

Bud Powell's "Glow" - that incredible tone that just sustains forever
M-S Recording - and Reverse M-S too...

On Teaching

Mixophrygian Augmented or: Why Scales Are For Fish

On Life In General

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