[Nate Najar]

So i was comparing some mics tonight and thought I'd try MS miking my
classical guitar. Schoeps cmc641 for m and 414 for S. I put the
schoeps capsule right on top of the 414. null of the 414 pointed in
the same direction as the schoeps capsule. Both mics into my
millennia hv3. go to 3 tracks of PT. schoeps into one track and the
414 goes to 2 tracks. Pan the 414 tracks hard left and right and
reverse the polarity of one of the tracks.

Sounds right doesn't it? well... if you listen to the 414 tracks by
themselves the left and right meters are equal. The schoeps track
soloed also obviously brings the meters equal. But you combine them
and there's some sort of phase cancellation- reduces the level of one
of the sides. But if you reverse the polarity of the M track it just
reverses the phase cancellation from L to R, and obviously if you
reverse the polarity of one of the S tracks you cancel out the whole
signal.

So what did I do wrong?

Nate

[Scott Dorsey]

Nate Najar wrote:

Sounds right doesn't it? well... if you listen to the 414 tracks by
themselves the left and right meters are equal. The schoeps track
soloed also obviously brings the meters equal. But you combine them
and there's some sort of phase cancellation- reduces the level of one
of the sides. But if you reverse the polarity of the M track it just
reverses the phase cancellation from L to R, and obviously if you
reverse the polarity of one of the S tracks you cancel out the whole
signal.

Right. This is because the soundfield in front of the mikes was louder
on one side than the other.

So what did I do wrong?

Nothing. Remember, the M-S pair is functionally identical to a pair of
coincident cardioids once it's decoded. Move sound source to the left
and the left channel gets louder.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Nick Brown]

Nate Najar wrote:

But you combine them
and there's some sort of phase cancellation- reduces the level of one
of the sides.

Where did you have the mics? Somewhere out in front of the 12th fret?

Was the imbalance in the level consistent with more sound coming from
the guitar body than from the neck? It may not be what you're after,
but as Scott says, it doesn't sound like there's anything wrong with
the mics or the decoding.

Like me you may well have put the middle mic exactly where you would
for a mono recording (i.e. where it sounds best in isolation) and
you're looking to add some side signal to give the sound a little bit
more sense of existing in space.

If you rotate the whole the mic array so that the stereo picture is
balanced, your middle mic won't then be pointing where you would
otherwise have put it. Since creating an accurate stereo image isn't
really my goal here I find it suits me just to leave the middle mic
alone, and rotate the side mic until either the image is correct, or
just until it sounds best (this usually means moving the null about 15
or 20 degrees towards the sound hole). You can of course make your own
judgement about whether the end justifies the means.

Cheers,
Nick

[Mike Rivers]

On Feb 18, 10:24 pm, "Nate Najar" wrote:

Both mics into my
millennia hv3. go to 3 tracks of PT. schoeps into one track and the
414 goes to 2 tracks. Pan the 414 tracks hard left and right and
reverse the polarity of one of the tracks.

Sounds right doesn't it? well... if you listen to the 414 tracks by
themselves the left and right meters are equal. The schoeps track
soloed also obviously brings the meters equal. But you combine them
and there's some sort of phase cancellation- reduces the level of one
of the sides.

Well, that's the way that stereo works. There's some phase
cancellation and it's not symmetrical in the room.

You might want to verify that you don't have a gain change in one
channel of the side mic. Pan both the inverted and non-inverted track
to the same side (or to the exact center) and see how well they
cancel. It should be perfect. But I suppose since DAWs aren't perfect,
there could be a sample or few offset between the two tracks since
they were recorded "simultaneously" (or so you thought).

If you don't get perfect cancellation, try using just one recorded
track, copy it to another track in the same position, and invert one.
That should be perfectly in phase.

[Nate Najar]

On Feb 19, 9:05 am, "Mike Rivers" wrote:
Well, that's the way that stereo works. There's some phase
cancellation and it's not symmetrical in the room.

You might want to verify that you don't have a gain change in one
channel of the side mic. Pan both the inverted and non-inverted track
to the same side (or to the exact center) and see how well they
cancel. It should be perfect. But I suppose since DAWs aren't perfect,
there could be a sample or few offset between the two tracks since
they were recorded "simultaneously" (or so you thought).

If you don't get perfect cancellation, try using just one recorded
track, copy it to another track in the same position, and invert one.
That should be perfectly in phase.

Thanks for the answers! Mike I do get perfect cancellation so the
side mic is ok. What surprised me is if you listen to the M mic by
itself the signal's centered and t s mic by itself is centered but
together I get a bump on one side. It must be as scott suggested that
i'm just getting more sound from one side than another. I've got the
array pointed near where the neck meets the body and about 12 inches
out. So I suppose the soundhole side is probably giving more signal
now that I think about it. I'll have to work more on placement.

Nate

[Mike Rivers]

On Feb 19, 9:16 am, "Nate Najar" wrote:

What surprised me is if you listen to the M mic by
itself the signal's centered and t s mic by itself is centered

That's to be expected because when you're listening to one mic, you're
listening in mono, or at least with the same signal sent to both
speakers. The only reason why it wouldn't be centered is if your
monitor system wasn't balanced. That it's centered is a good thing.

together I get a bump on one side. It must be as scott suggested that
i'm just getting more sound from one side than another. I've got the
array pointed near where the neck meets the body and about 12 inches
out.

In that position, you're probably getting more sound hole sound than
string sound, and what comes out of the sound hole has more energy due
ot the greater low frequency content so it would look unbalanced on
the meters. That's often a decent position for a mono mic because the
overall frequency balance is pretty good there.

How does it sound? Does it sound like the guitar is too wide, with
more bass on one side than the other? If so, you need to move the mic
either further away if the room isn't a problem, or more toward the
sound hole. But it might get too boomy if you go too far.

The trick is, as usual, to listen while you're positioning the mic. If
you have some well sealed headphones, you might try raising the mic up
so you can play standing up, then move side to side while you're
playing to find a spot where things sound balanced and centered. Or
just make a series of test recordings sliding your chair over a few
inches each way from your starting position.

[Scott Fraser]

Remember, the M-S pair is functionally identical to a pair of
coincident cardioids once it's decoded.
"C'est un Nagra. C'est suisse, et tres, tres precis."

Last week I decided to do a solo guitarist in MS instead of my usual
coincident or near coincident approach. A TLM193 was the Mid, a C414
in figure 8 with the front aiming left was the Side, out about 4 feet
in front of the guitar. Using the MS decoder plug in in Digital
Performer it just didn't sound right at all, & a stereo scope
confirmed essentially random phase, looking very much like spaced
omnis. Switching out to an XY pair of TLM193s restored a familiar
sense of stereo & a very familiar stereo diagonal pattern on the
scope. So why didn't the MS equal XY when decoded? Is this plug in not
implemented right? I didn't try manually setting up an MS decoder with
a duplicate Side track, but how can it be done wrong in a plug in?

Scott Fraser

[Federico]

Some plugins want a M/S input to decode right.
But some plugins that want S/M to decode right!!
Be sure you check that.
F.

[Scott Dorsey]

Scott Fraser wrote:

Last week I decided to do a solo guitarist in MS instead of my usual
coincident or near coincident approach. A TLM193 was the Mid, a C414
in figure 8 with the front aiming left was the Side, out about 4 feet
in front of the guitar. Using the MS decoder plug in in Digital
Performer it just didn't sound right at all, & a stereo scope
confirmed essentially random phase, looking very much like spaced
omnis. Switching out to an XY pair of TLM193s restored a familiar
sense of stereo & a very familiar stereo diagonal pattern on the
scope. So why didn't the MS equal XY when decoded? Is this plug in not
implemented right? I didn't try manually setting up an MS decoder with
a duplicate Side track, but how can it be done wrong in a plug in?

My bet is that the space between the mikes was way too great for phase
coherency. Try a physically smaller mike and get it right on top of the
C414. It doesn't take much distance to make things go wrong at high
frequencies.

And, of course, be sure the C414 is working right and has a good null in
figure-8.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Fraser]

My bet is that the space between the mikes was way too great for
phase
coherency. Try a physically smaller mike and get it right on top of
the
C414. It doesn't take much distance to make things go wrong at high
frequencies.

They were as close as the grilles physically allow. That might put the
center of each diaphragm an inch & a half apart, vertically.

And, of course, be sure the C414 is working right and has a good
null in
figure-8.
--scott

Well, it sounds like a 414, so there's an issue about it sounding
right to begin with.
What amazed me was that it didn't sound (or look) like poor XY. It was
like spaced omnis.
I'll go back & do the MS decoding by hand & see if the MOTU plug is
wrong.

Scott Fraser