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Author Topic: Oddball microphone techniques  (Read 57559 times)

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Re: Oddball microphone techniques
« Reply #345 on: December 04, 2017, 12:14:42 PM »
Perusing an old thread, I came across a comment that seems appropriate for this thread:

Quote
The not at all simple alternate answer which potentially could help adjust for being off-center has to do with adjusting the microphone configuration in combination with rotating the stand.  It's probably far more trouble than it's worth, would be hard to do precisely in the field, and is not something most tapers would want to try, but is interesting to me technically.  I won't go into it here in too much depth, but it has to do with adjusting the angle of each microphone so they are no longer in a symmetrical arrangement with the center axis of the microphone array.  Essentially, one microphone is moved forwardof the other, and that accomplishes something similar to the delay thing I described previously, "at the microphone array" itself.

That's based on the work of Michael Williams which explores the inter-relationship between pickup pattern, angle, spacing and position of a pair of microphones.  It's how he goes about "linking" multiple microphone pairs together to form multichannel surround recording arrays which are capable of seamless playback imaging between across each microphone/speaker pair sector, without gaps or overlaps.  His papers on Multi-Microphone Array Design (MMAD) explain this in depth, but are more technical than most tapers here will care to get into.

This was in the context of a question about what to do when setting up off-center from the sound source.  The bolded part has me most intrigued.  I find it really distracting when I'm listening and the whole sound is noticeably off-center.  Obviously sometimes we can't set up at the center line for whatever reason.  I've found that just raising the level of the more "distant" channel is often unsatisfactory...maybe because the volume level doesn't make up for time of arrival differences in the channels?  So, I'm curious about the practical application of the idea hinted at in the quote above.  If we're talking about a near-coincident stereo pair, would putting one of the mics closer to the sound source help mitigate being off-center more than simply raising the gain of one channel?  I'm guessing that the mic on the more distant side would need to be moved closer.  How much of a change in location are we talking about, though?  If we think of it in terms of just a simple PAS config, would each of the mics be pointed at the stacks after adjusting the forward location of the one mic?  Or before making that adjustment?
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Re: Oddball microphone techniques
« Reply #346 on: December 04, 2017, 01:40:55 PM »
Yes, level balancing afterwards is always helpful but can only do so much.  The practical solution at the show is to close your eyes and rotate your head to find the most balanced auditory center direction by ear, then rotate the entire mic-stand to match.   Don't trust what your eyes tell you, as often the acoustic center will not match the visual center.  Perhaps counter-intuitively, this technique will tend to point the microphones toward the louder PA, or more toward the near-side PA stack when located off-center - that is to say it will point the mics further away from the visual center and not towards it.  The result however will be a much more acoustically balanced recording.

I think this is the William's paper in which he discusses the microphone offset technique- http://www.mmad.info/Collected%20Papers/Multichannel/4997%20New%20York%201999%20(31%20pages).pdf, as one technique of several used to achieve "critical linking" between the individual recording angle segments in multiple microphone arrays - the idea being to have each segment align with the next along it's shared Stereo Recording Angle edge without excessive over-lap or a gap between them.  Obviously that's a rather involved process to figure out, but sheds light on what's going on acoustically.  You can see how simply rotating the entire microphone array to point at the apparent auditory center is sort of doing something similar, if less extreme.

^ That paper and many of his others is made generously available for non AES members via Michael William's website- http://www.mmad.info/

« Last Edit: December 04, 2017, 01:42:42 PM by Gutbucket »
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