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Old September 6th, 2006, 05:09 PM   #16
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Originally Posted by Jay Massengill
Although personally I wouldn't put them that far apart for a spaced stereo recording, even though some do it that way. While the 3 to 1 rule is very important for placement of mics in a multi-mic setup, putting that much space between two mics for a spaced stereo pair would lead to a very large phase difference as well as an exaggerated stereo spread.
I'd stick with 3 to 10 feet depending on the size of the ensemble for spaced stereo, although I'd really be more likely to use a coincident or near-coincident pair because it's easier to get reliable results, especially for video work.

I'm just guessing here because I'm not an acoustic engineer by any stretch of the imagination, but I suspect the 3 times rule comes about precisely because it does indeed introduce such large phase differences that the instantaneous signal at each mic is of parts of the waveform sufficiently distant from each other in time that they they don't interact strongly to produce the comb filtering effects. The frequency of a complex audio waveform varies wildly over time and so the frequency at any given instant is very different from that of parts of the wave very close to it in time. Two 1000Hz notes with their zero crossings slightly displaced with respect to each other will produce strong phase effects but but displacing a 3000Hz tone in time with respect to the zero crossings of a 1000Hz tone won't affect the resulting beat notes very much. If the waveform arrives at the 2nd microphone at a very short interval after it arrived at the first mic, we're going to have a situation like the first example. But if the mics were further apart, the waveform hitting the 2nd mic at this instant would come from sufficently earlier in time from the one now hitting the first mic that it would more resemble the second example. Of course I could be totally wet with my theory but I've seen the 3:1 rule mentioned in too many different sources not to think there's some good reason for it.

Here's my logic - see if it makes sense to you. Let's say we have a source 10 feet directly in front of mic A and mic B is 3 feet to the side of A. The source->A distance is 10feet, the source->B disance is 10.4 feet. That translates to an arrival time difference of 0.4millseconds, for most notes resulting in mixing two parts of the same cycle of the two signals. But if the source->A is 10 feet and the 3:1 rule is applied, mic B is 30 feet to the side and the source->B distance is 31 feet and the arrival time difference is 20 millisec, so far apart that it's a time delay but not a phase shift with the result sounding more like a reverb effect and less of a comb filter effect.

Also, remember that we're not talking about any problem with closer spaced when the two mics are listened to in stereo - spaced omnis or cardioids can be very good in stereo. The problem only rears its head when the signal is collapsed to mono, exactly the same situation that you're talking about when you mention its great important in a multi-mic setup.
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Old September 6th, 2006, 08:55 PM   #17
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There is quite a bit of experience with the decca tree, or modified decca tree and dealing with mono.

One variation inthe setup is to have the center mic or mics be forward one half the distance between the outer mics.

In general coming from the audioi world, it was recommended to monitor the signal in a mono mode to check for issues. If there was a problem, usually the first thing that was done was to move the outside mics closer together. The other thing done was to raise the level of the center mics. The panned setup was left mic panned left, right mic panned right and the center mic or mics to be centered.

The distance rules were really designed for much closer in micing situations within a few feet. In a concert once you are back the distances we are talking about the origniating sound and the early reflections off the side surfaces etc, all come into play. It is these side surface what are called early reflections that have a big impact on how the musicians sound. The purpose of the decca tree or any side mic pickup is to capture and use these sounds.

As always you have to use your ears, and remember that monitoring via headphones is NOT a good idea once you get to the more complex multi mic setups, as the headphones isolate left and right to the respective ears, when speakers do not. In general most of the problems I have seen are where the monitoring was done over head phones.

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Old September 7th, 2006, 04:02 AM   #18
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That's also a reason M/S micing is a good choice for recording stereo destined for fillm, video, and FM broadcast - with mixed to mono the side mic disappears leaving only the mid mic as a clean mono signal.
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Old September 7th, 2006, 09:23 AM   #19
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Just record M and S. The M signal is the mono signal you want - no further fiddling required. L and R, if required, are obtained by matrixing in post and you have control over the amount of separation you want which you don't have if you use the matrix in the mic (it may give you multiple settings but you can't change your mind after the fact).
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Old September 7th, 2006, 02:05 PM   #20
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A very important part is to look at the the instruments you're recording, observe where does the sound radiate from. And when positioning spot mics you are trying to capture most of the direct sound, as oppose to ambience, or room. Which means, it has to be fairly close to the section, you didn't tell what the wind section was composed of. Watch out for the flutes, for classical stuff try not to point the mic too directly at the mouthpiece, you get this pffff sound, for jazz recordings that is a must. Experiment with miking the clarinets, don't know about you but I could never get them to sound mellow. See if you like the sound. Oh and last tip, tell the musicians to "project as if in a concert with audience."

As a funny joke, how do you get a cello to sound nice?
Sell it and buy a violin.

Sometimes that's just the way an instruemtn sound, can't fix it.
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Old September 10th, 2006, 05:31 AM   #21
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Originally Posted by Jerry Jesion
I would like some suggestions on how to mic a wind band (up to 75 members). I have an M/S stereo condenser mic (Studio Projects LSD 2) which works quite well, but players in the back sound distant. I have tried sm57s on either side for fills which helped somewhat. Should I place mics among the band members? If so how many and where should they be placed? Any suggestions on which mics to use? I usually have good cooperation from the conductor but sometimes it would not be possible to place mics in the band. Any suggestions for this possibility? I have a 12 channel recorder so the number of inputs is not a limitation.


Get some altitude (above the band) and move back to a position from which you can hear a good balance. With 75 instrumentalists, you will lose some of the back row.


You can try a Decca Tree array of omnis for the overall sound and add in some zone mics or spot mics. Zones for similar instruments, spots for individual instruments.


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