I am experimenting with M-S mic technique and need some advice on relative
levels between the mid and the side tracks.

I recorded a classical chamber music group using an AKG c-34 stereo mic (
http://tinyurl.com/56clz ). The capsules in the mic are coincident and
arranged at 90° to each other. The front facing capusule was set to cardiod
pick-up pattern and the the "side" facing capsule was set to figure-8
pattern.

When checking levels, I noticed that the mid capsule's response was
significantly less than that of the side capsule despite pre-amp levels
being set identically. At the time I left the pre-amp levels as they were
since the SNR was such that I could boost the signal afterwards with out an
increase in noise floor.

What I am wondering is now that I would like to transform the M-S pair into
a LR stereo downmix, is it necessary for me to boost the signal of the mid
track relative to the side track?

If you could cc your replies to me via e-mail as well, this would be greatly
appreciated.

Thanks in advance,
Theo

Theo,

I've never used a C 34, but I'm a little surprised that its figure-8
setting would be so much more sensitive than its cardioid setting. You
may have some other kind of problem there; I'd suggest that you look
for an explanation of the discrepancy.

Anyway, when matrixing from an M/S recording to left/right stereo, you
should definitely have some way of adjusting the levels of the "M" and
"S" signals that you're feeding into the matrix. First of all these "M"
and "S" signal levels must suit the matrix--neither overloading its
circuitry nor being so low in level that the result is noisy.

But yes, as long as the signal voltages aren't too high or too low for
your matrix circuitry, you absolutely can adjust the two signals
relative to each other. That's one of the main advantage of M/S
recording: the amount of "S" relative to the amount of "M" is a direct
control over the apparent stereo width of the recording, and you don't
have to decide this setting while you record (where you may not have
good monitor speakers available)--you can set it afterwards, when you
matrix to L/R stereo.

One way to do this is to start by feeding only a small amount of "S"
signal into the matrix, then gradually bringing it up in level. If you
do this, you can feel the image widen from mono to a reasonable stereo
spread--and then beyond, if you push the "S" level too far (things will
start to get "phasey," particularly when sound sources at either edge
of the sound stage are prominent).

Usually I find that there isn't very much doubt (on any given playback
system, at least) about where the M vs. S levels should be set for any
given recording, since the amount of hall reverberation generally
increases as the stereo width increases, and there is a certain blend
of spaciousness and clarity that feels persuasive, while anything else
seems too far in one direction or the other.

But please don't feel that you have to maintain the relative
sensitivities of the two halves of your microphone; that's just a
physical parameter of your microphone, and in this case, I would even
consider it a little suspicious as I said before. Much more often the
"S" microphone is a little less sensitive than the "M" microphone, and
in addition, picks up less acoustic energy because it receives so
little direct sound.

In any event the capability of varying "M" vs. "S" gain at the matrix
inputs is one of the keys to making good use of any M/S recording.
--best regards

In article writes:

I am experimenting with M-S mic technique and need some advice on relative
levels between the mid and the side tracks.

Simple - what sounds right is right.

When checking levels, I noticed that the mid capsule's response was
significantly less than that of the side capsule despite pre-amp levels
being set identically.

Are you sure you didn't have the carioid capsule facing backwards? Or
that the microphone was working correctly? It's unusual that you'd
have more "side" sound pressure than "direct to the front" sound
pressure.

What I am wondering is now that I would like to transform the M-S pair into
a LR stereo downmix, is it necessary for me to boost the signal of the mid
track relative to the side track?

First off, are you aware that when you "downmix" you need to both add
and subtract the mid and side mics? As a starting point, it's
conventional for the in-phase and out-of-phase side channels to set
about 6 dB below the mid channel. But to use your ears, start with the
mid signal (only) set so that you have plenty of headroom, then bring
up the + and - side signals together (equally) while listening. Stop
when you hear good stereo, and if you hear a hole in the middle, stop
and back up until the hole fills in.

If the mid signal by itself doesn't sound really good (it will be mono
of course) then something is very wrong with the mic or the recording
setup.

If you could cc your replies to me via e-mail as well, this would be greatly
appreciated.

That's a paid service. Read the newsgroup and learn.

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

I know this sounds stupid, but are you sure you got the right outputs for
middle and side? The pattern box on the C-34 can be a bit ambiguous
sometimes. If your pres are set with the same gain, you can expect several
dB difference in level between middle and side (the middle always being
higher). Either that or your mic isn't working properly.

To get M-S to decode and sound "right" you are going to have to have your
sides look like a lower level than the mid. If your sides get too high, the
fact that it is out of phase will begin to really show.

--Ben

--
Benjamin Maas
Fifth Circle Audio
Los Angeles, CA
http://www.fifthcircle.com

Please remove "Nospam" from address for replies

"Theodore Chan" wrote in message...
I am experimenting with M-S mic technique and need some advice on relative
levels between the mid and the side tracks.

I recorded a classical chamber music group using an AKG c-34 stereo mic (
http://tinyurl.com/56clz ). The capsules in the mic are coincident and
arranged at 90° to each other. The front facing capusule was set to
cardiod
pick-up pattern and the the "side" facing capsule was set to figure-8
pattern.

When checking levels, I noticed that the mid capsule's response was
significantly less than that of the side capsule despite pre-amp levels
being set identically. At the time I left the pre-amp levels as they were
since the SNR was such that I could boost the signal afterwards with out
an
increase in noise floor.

What I am wondering is now that I would like to transform the M-S pair
into
a LR stereo downmix, is it necessary for me to boost the signal of the mid
track relative to the side track?

If you could cc your replies to me via e-mail as well, this would be
greatly
appreciated.

Thanks in advance,
Theo

Theodore Chan wrote:
I am experimenting with M-S mic technique and need some advice on relative
levels between the mid and the side tracks.

Season to taste.

When checking levels, I noticed that the mid capsule's response was
significantly less than that of the side capsule despite pre-amp levels
being set identically. At the time I left the pre-amp levels as they were
since the SNR was such that I could boost the signal afterwards with out an
increase in noise floor.

A reasonable starting balance if the mid is a card would be
to adjust the mid level when pointing at the source, rotate
90 and set the side level 6 dB down from that.

That will give you virtual mics pointing at +-45 degrees
when matrixed to LR. Increasing the side level splays that
angle and decreasing it closes it.


What I am wondering is now that I would like to transform the M-S pair into
a LR stereo downmix, is it necessary for me to boost the signal of the mid
track relative to the side track?

Boost or cut to whatever extent you wish to get the kind of
stereo image you want. Best use your ears for this.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

Just thought. maybe use M/S to capture the kit from out front enough and high
enough not to get cymbal shimmy. Toss something in the kick, maybe add a
snare mic?

Regards,

Ty Ford





-- Ty Ford's equipment reviews, audio samples, rates and other audiocentric
stuff are at www.tyford.com