DOUBLE M-S: A BRIEF HISTORY AND ITS BASIC IMPLEMENTATION

By Curt Wittig

PREFACE
Although this technique has been in use and gone through many
refinements by its users for more than a decade, none of us has ever sat
down to write about it in much depth, but simply passed it on to others
in person and in actual use. Therefore what appears below is still a bit
sketchy, having gotten started being written about at all only when its
implications for music surround recording have recently revealed
themselves.

Doing a more detailed job of writing about it is now a priority and
underway, but in the meantime I hope the following will be useful.

DOUBLE M-S: A BRIEF HISTORY AND ITS BASIC IMPLEMENTATION

Double M-S is a microphone technique I helped develop with Neil Muncy
when we were teaching in the NPR Music Recording Workshops in the 1980s
with David Moulton, Paul Blakemore and several NPR staff members,
particularly with Skip Pizzi. It has been used for stereo recording for
more than a dozen years, and is now finding new use as a very effective
way to create compellingly believable front and rear stereo soundfields
in a variation of 5.1 stereo surround adapted for music recording, tied
together with a sixth captured overhead channel that creates a tangible
and very stable three-dimensional stereo surround illusion.

Its original implimentation for two-channel stereo was developed in
those National Public Radio workshops (now unfortunately defunct) as a
solution to the problem of making stereo recordings in a simple manner -
i.e. that could be set up quickly with a minimum of fuss and visual
clutter when making live and recorded classical music broadcasts - and
whose musical balances from the soundstage and the ambient responses of
the hall wouldn't collapse in mono as they so often did on so many of
their own as well as on many commercial recordings when heard by a large
segment of the radio audience who still listened in mono at that time. We
named that technique Double M-S, and I and many others have continued to
use and refine it ever since for more broadcasts and albums than I can
now count.

The idea is elegantly simple, involving one M-S microphone primarily
for direct sound from the soundstage, and a second one at or just beyond
the critical distance of the room but facing away from the soundstage
into the reverberant field. If you are not familiar with the concept
"critical distance", it's that point in the room where direct sounds and
their early reflections from the soundstage and reflected sounds from the
revereberant field arrive at roughly equal intensity. Placing the ambient
microphone there or beyond - though not so far that a "slap" or "second
attack" is obviously heard in it when mixed with the front stereo image -
helps insure that any leakage from the direct sounds from the stage is
sufficiently weak to keep it from dominating the ambient sounds. The idea
is to be able to create a controlled stereo mix of direct and ambient
information with a minimum of phase and time domain conflicts.

The result in a good room is a clear, spacious sounding recording with
good imaging and presence, a solid low end, and more interesting ambience
- or at the very least, more easily controllable in the mix - than can be
obtained from, for example, a "Blumlein" (usually meant to mean "crossed
figure-of-eight") stereo array used alone. The technique does not
preclude the judicious use of accent mikes, panned into place and just
loud enough to balance the presence of weak musical elements.

In placement of the front M-S microphone, care should be taken to
include among the early reflections the very first of them all - i.e.
those from the floor - without which the character of the sound of many
instruments is emasculated, particularly woodwinds, idiophones, and low
strings. In fact when a "good shot" at the floor from the soundstage
microphone position is available even with ensembles all the way up to a
full symphony orchestra, not very many such accents mikes are usually
needed when the stage isn't so crowded that the floor isn't able to do
its job either for that microphone, or for that matter for the response
of the hall itself.

I was the first in our group to find an opportunity to actually make
such a recording, though it wasn't yet full "Double M-S" as defined
because all that was available for the backwards-facing array was an X-Y
pair of cardiod Neumann KM-84s. The front M-S arrangement wasn't ideal
either, but just a pair of U-87s head-to-head and a simple M-S matrix.
Nonetheless, the result was so startlingly beautiful that there was
nothing to stop its progession in my own use of it to a pair of AKG
C-422s, then to a pair of ST-250 Soundfields. It continues to be a viable
way to make very satisfying stereo recordings that I've now used for
about 100 albums and countless live and recorded concert broadcasts in
the US and Mexico. Finding that its principals work so well unaltered as
part of stereo music surround simply by recording the outputs of the two
M-S microphones as seperate stereo pairs for front and rear has been
quite a thrilling discovery.

Besides being taught in the Music Recording Workshops, Double M-S was
also presented at a well-attended workshop at the 1987 AES convention in
New York, and continues to be taught privately and in the Production
department of Interlochen Public Radio (IPR) at the Interlochen Arts
Academy in Michigan.


(c) 1997 by Curt Wittig
Version 1.02

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