Stereo AB - Mono compatibility - classical market?

**Lee Blaske** · 02-18-2011, 10:52 PM

Originally Posted by hbphotoav

Good survey of stereo mic techniques: http://lossenderosstudio.com/stereo-...techniques.php

Great link. Thanks.

I can see I'm going to have to acquire a fancy pair of small diaphragm cardiods to experiment with a a lot of these.

**hbphotoav** · 02-19-2011, 04:34 PM

I posted a comparison over on GS from an organ concert with four pairs... MKH8040 in ORTF, Advanced Audio CM-28 (tube, with omni caps) and DPA4061 in a wide A/B (3m apart), and a Quite Tasty Brauner VM-1S in XY (tube, LDC... and talk about your uncompromised fold-down). There are 320mbps clips and a "name-that-mic" exercise. Lots of informative chatter about patterns, positions and so forth. See it at:

http://www.gearslutz.com/board/remot...requested.html

And another with a comparison of a 40cm omni spread (Gefell M296) and a 1m pair or 4061s on an orchestra job:

http://www.gearslutz.com/board/remot...1-comparo.html

Might be informative for you, as well.

Cheers.

HB

**Lee Blaske** · 02-27-2011, 04:46 AM

OK, I had a little time to delve further into examining some of my recent AB recordings (examining them with a vector scope, etc.) and discovered something really weird. I inserted the Waves S1 Shuffler, and flipped the phase of one side 180 degrees. Voila! Nicer stereo image (a little more bass), and mono compatibility problem solved (I used an ITB mono plug on the master, just to rule out any problems in monitor speaker wiring - which is fine, BTW). Went back and checked and double checked all the cables I used on the live recording, and everything is wired correctly.

There are no phase switches on the equipment I used. At this point, I wonder if either one of my DPA 4009 mics is wired incorrectly, or the DPA HMA4000 preamp, or my Metric Halo 2882+ DSP.

I don't think I want to take the DPA mics apart. Can anyone recommend a sure-fire practical test? I'm thinking of setting them both up in front of a single speaker playing back a test tone.

For you guys who know a lot more about AB recording, is it possible that in this situation, where I had the two mics spaced about 40 cm apart, I could have a situation where flipping the phase of one mic would give me a dramatic improvement in perceived stereo image, and good mono compatibility?

In that particular recording environment, assuming the same mic distance from performers, do you think it's possible that a different spacing could totally correct the mono compatibility situation?

It just doesn't seem right, but at the moment, flipping the phase of one mic is doing the trick.

I've got to do more checking and get to the bottom of this.

**Gio** · 02-27-2011, 05:05 AM

If you are absolutely certain all your cables ( and monitor speakers) are wired correctly, here's what you can do to check the gear without buying anything.

Don't use a tone through a speaker. Set up one mic and pre. Record a single clave strike or something similarly sharp and percussive. Look at the waveform in your DAW. If the wave goes up first, your OK. If it goes down, something is flipped somewhere. Swap the mic and try again. If the result is the same, check which pin is hot at the the pre. Rinse, repeat. If everything checks out, then it's something else.....

**3daudioinc** · 02-27-2011, 05:20 AM

Better yet, get one of these and put your mind at ease.

http://www.sweetwater.com/store/detail/Cricket/

**Lee Blaske** · 02-27-2011, 05:29 AM

Originally Posted by Gio

If you are absolutely certain all your cables ( and monitor speakers) are wired correctly, here's what you can do to check the gear without buying anything.

Don't use a tone through a speaker. Set up one mic and pre. Record a single clave strike or something similarly sharp and percussive. Look at the waveform in your DAW. If the wave goes up first, your OK. If it goes down, something is flipped somewhere. Swap the mic and try again. If the result is the same, check which pin is hot at the the pre. Rinse, repeat. If everything checks out, then it's something else.....

Brilliant. That'll help me pinpoint it.

**Lee Blaske** · 02-27-2011, 05:30 AM

Originally Posted by 3daudioinc

Better yet, get one of these and put your mind at ease.

http://www.sweetwater.com/store/detail/Cricket/

That looks really handy. I'm going to have to get one of those.

**Gio** · 02-27-2011, 05:31 AM

Originally Posted by 3daudioinc

Better yet, get one of these and put your mind at ease.

http://www.sweetwater.com/store/detail/Cricket/

Well, I did offer the free version!

In that particular recording environment, assuming the same mic distance from performers, do you think it's possible that a different spacing could totally correct the mono compatibility situation?

I would think that it would make some difference.

**Lee Blaske** · 02-27-2011, 04:27 PM

Originally Posted by Gio

I would think that it would make some difference.

Thing is, it''s not some difference. It's night and day difference. I'm just about to set up and test the whole rig. I hope I can get to the bottom of this, and I really hope I find a problem somewhere.

If it turns out that everything is correct polarity wise, and that flipping the polarity of one of the AB mics still makes a huge difference, that's going to mess with my mind.

**Scott Fraser** · 02-27-2011, 05:57 PM

Originally Posted by Lee Blaske

Thing is, it''s not some difference. It's night and day difference. I'm just about to set up and test the whole rig. I hope I can get to the bottom of this, and I really hope I find a problem somewhere.
If it turns out that everything is correct polarity wise, and that flipping the polarity of one of the AB mics still makes a huge difference, that's going to mess with my mind.

Any time you have a non-coincident array, meaning any spacing other than XY, MS or Blumlein, you have certain frequencies cancel due to differing arrival times, i.e. phase cancellation. The frequency affected is a function of the distance of the spacing. It's unavoidable, just physics. The wider the spacing the lower the frequency of the cancellation. Sounds to me like you ended up with a spacing which cancels a low enough frequency that you're losing all the beef. There are a couple techniques which you might try for better mono as well as realistic stereo width. One is to space the mics no more than the width of human ears, so about 6 - 7 inches. This is near-coincident spacing & moves the phase cancellations up above 5k or so where no fundamentals occur & there is more latitude for phase error & the resulting timbre shift. A variation on this is the use of a baffle, such as a Jecklin disk or similar dummy head type element between the omnis. These are varying aspects of HRTF stereo which are quite natural and sum to mono pretty well.

Scott Fraser