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Author Topic: Off-center setup/config for specific room  (Read 1528 times)

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Offline heathen

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Re: Off-center setup/config for specific room
« Reply #30 on: January 18, 2018, 11:21:43 AM »
When I'm in similar off center positions taping off a stereo (or 2 stack array) I use A/B and choose between cards and hypers based on distance. With both mics mounted parallel on the bar, 6" or so apart, I aim them at the center of the stage. By doing this both mics will get the same basic signal from primarily the closest stack. But, because of the slight time delay between the mics, there is just enough of a difference between channels to give a limited illusion of stereo, not ideal but better than just pointing directly at one stack, IMO.

Are you keeping the bar itself parallel to the edge of the stage, or rotating the whole thing to aim at the center of the stage?
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Offline Gutbucket

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Re: Off-center setup/config for specific room
« Reply #31 on: January 18, 2018, 01:04:56 PM »
The linked example using standard mic setups from that room and similar situations elsewhere sound good, so that's the obvious and simple path to take for this specific situation and a good starting point.

But furthering the more general discussion of far off-center location..

When I'm in similar off center positions taping off a stereo (or 2 stack array) I use A/B and choose between cards and hypers based on distance. With both mics mounted parallel on the bar, 6" or so apart, I aim them at the center of the stage. By doing this both mics will get the same basic signal from primarily the closest stack. But, because of the slight time delay between the mics, there is just enough of a difference between channels to give a limited illusion of stereo, not ideal but better than just pointing directly at one stack, IMO.

Are you keeping the bar itself parallel to the edge of the stage, or rotating the whole thing to aim at the center of the stage?

A parallel spaced microphone arrangement is a good approach, using time-of-arrival rather than signal level for stereo difference when the directional balance at the recording position is askew.   

Combining a few of these ideas so they work together, here's an approach I'd like to hear-

>Use an AB spaced parallel microphone arrangement.
>Orient the AB array axis with respect to the apparent acoustic center (mic-bar perpendicular to a line pointing at that apparent acoustic center - the point it with closed eyes thing).
>Use very directional mics like hypers or figure-8's and point them at the PA on the opposite side (cardioids and probably supercards will not have enough off-axis sensitivity difference across their forward hemisphere for the near-side/far-side balancing part of this to work).

You then have a sort of AB parallelogram microphone arrangement.  The mics remain parallel to each other, but are no longer perpendicular to the mic bar.  The idea is that we are no longer using signal level difference based on angle difference between mics for stereo image (AB), but are using the microphone's pattern sensitivity to reduce the level of pickup from the near-side PA relative to the on-stage sound and far-side PA.   That can only work if the two mics are oriented parallel to each other and directional enough that the level differences arriving from different angles across the stage are somewhat reduced by the near-side PA being off-axis to both mics and the far-side PA being on axis to both mics.  It's a special PAS condition, pointing at the opposite side.

>We get stereo interest and sense of space from the AB spacing.
>The image remains centered because the energy in each channel is about the same (the pointing the whole array at the apparent acoustic center thing).
>We get a more balanced pickup of sources in the room by reducing pickup sensitivity for the close sources which are more off-axis, and increasing pickup sensitivity towards the far-side sources which are on-axis, based on the parallel arrangement of directional mics.
>We get some corrective image balance by effectively having sound from the far side arriving at the left mic prior to its arrival at the right mic, while the sound from the close-side arrives simultaneously at both mics.  The left mic is slightly forward of the other mic when viewed from the far side.  (This is a Michael Williams MultiMicrophoneArrayDesign MMAD principle)

Here's a plan-view sketch, looking down from above-

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Offline Gutbucket

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Re: Off-center setup/config for specific room
« Reply #32 on: January 18, 2018, 01:05:14 PM »
^
Drawing is not to scale.  The PA speakers are the red squares, the walls are the red lines.  AB microphone arrangement shown with the mics parallel and facing the far-side PA.  Left PA sound arrival vectors are green.  Right PA arrival vectors are blue.  Right sidewall PA reflection vector is pink.

Notice that the far-side PA is on-axis to both mics and the near-side PA is off-axis to both mics, if the mics are directional enough, that serves to "even out pickup across the stage" somewhat. I'm using figure-8s on the mic bar to maximize the sensitivity difference between on-axis and off-axis across their front hemisphere as much as possible (because figure-8 with sideways facing nulls has the tightest forward lobe of any 1st order microphone pattern, a cardioid isn't going to have enough off-axis rejection until you get around to the back-side, and even a supercard may not provide enough sensitivity difference across the front, given the difference in angle to the two PAs which we're trying to leverage to our advantage).

Might be able to further the off-center balancing nature of the array by pointing the mics even further outside of the left PA speaker, which pushes the near PA arrival angle closer to the side-nulls of the 8s.  Probably want to keep the figure-8 sideways facing null pointing behind the sidewall reflection point from the near-PA, and that limits how far outside of the left PA you can point the mics.  Regardless of how the mics themselves are pointed to take advantage of their directivity, or what polar pattern is used, the mics are parallel to each other and the mic bar is always perpendicular to the apparent acoustic center.

I suggested something similar using parallel figure-8s many years ago in another off-center thread.  Hypers or supercards might work too and are the obvious thing to try as more tapers have a pair of them.  Fun to think about.
« Last Edit: January 18, 2018, 01:08:46 PM by Gutbucket »
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Offline heathen

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Re: Off-center setup/config for specific room
« Reply #33 on: January 18, 2018, 01:54:37 PM »
I would definitely try something like that this weekend, as there will be other people taping, but I don't have a pair of hypers or figure 8s.
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Offline rocksuitcase

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Re: Off-center setup/config for specific room
« Reply #34 on: January 18, 2018, 02:04:25 PM »
Might be able to further the off-center balancing nature of the array by pointing the mics even further outside of the left PA speaker, which pushes the near PA arrival angle closer to the side-nulls of the 8s.  Probably want to keep the figure-8 sideways facing null pointing behind the sidewall reflection point from the near-PA, and that limits how far outside of the left PA you can point the mics.  Regardless of how the mics themselves are pointed to take advantage of their directivity, or what polar pattern is used, the mics are parallel to each other and the mic bar is always perpendicular to the apparent acoustic center.

I suggested something similar using parallel figure-8s many years ago in another off-center thread.  Hypers or supercards might work too and are the obvious thing to try as more tapers have a pair of them.  Fun to think about.
I second this idea and present some anecdotal support for the acoustic hypothesis: We used to tape at a venue in Dallas, Club daDa the main room at the time was similar to this. Bar on one side, SBD on the other side, stage at one end of the short side of a rectangle. We/I ran Beyer Hyper cards (M201-c) in XY (typically 90) with them aimed straight forward no tilt toward the stage as the room was pretty narrow anyway, from about two feet in front of the soundboard (~8 feet from rear wall) and 2-3 feet from the side wall. Many of those recordings are excellent or at least worth listening all these years later. Some experienced listeners have told me the recordings seem "monophonic" which is what would result typically from that pattern in that location. So, aiming as you suggest might have brought out some space or depth.
« Last Edit: January 18, 2018, 09:04:45 PM by rocksuitcase »
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Offline Gutbucket

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Re: Off-center setup/config for specific room
« Reply #35 on: January 18, 2018, 05:35:12 PM »
I think so.  What I describe above (angling across the stage at the far side) only works with spaced parallel mics, as any angle between mics causes the off-center source balancing part of the arrangement to fail as the loud PA on the nearside will immediately dominate the mic angled more towards it.  It's the spacing that makes it stereoized.  Your way-off-center, close-to-the-wall X/Y setup leveraged the point at the apparent acoustic center thing, with the mic angles symmetrical to the apparent acoustic center, probably taking advantage of the reflection off the sidewall in the mic angled toward that side.
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Offline Gutbucket

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Re: Off-center setup/config for specific room
« Reply #36 on: January 18, 2018, 05:37:49 PM »
I would definitely try something like that this weekend, as there will be other people taping, but I don't have a pair of hypers or figure 8s.

Go ahead and give it a try with cardioids if you want to give it a go and aren't worried about taking the risk.  Cardioids might not help as much with increasing the level of pickup of the far-side verses the near-side in the same way as a 8's or hypers, but the image should remain balanced and the angled-but-parallel arrangement should still be beneficial.  If you do, please report on how it works out.  If nothing else it may prove me a total fool!
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Offline heathen

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Re: Off-center setup/config for specific room
« Reply #37 on: January 18, 2018, 06:01:36 PM »
I'm all for experimenting, so let me make sure I'm understanding what you're suggesting.  The scale of the attached image is obviously distorted, but is this the general idea you're referring to?
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Offline Gutbucket

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Re: Off-center setup/config for specific room
« Reply #38 on: January 18, 2018, 07:31:30 PM »
Basically yes. I had to click on the image to see the 90 degree indication of the mic-bar to the acoustic center, as it looked like the mic bar was turned more so as to be perpendicular to center stage.  It will probably be closer to perpendicular to the right PA or just inside of it, but again- trust your ears in determining that acoustic center orientation, not your eyes.  And orient the mics so they are parallel to each other.  You don't want the left one toe'd in more than the right or the image of the louder Right PA will shift towards that side, or the other way around.  Keep the angle the same on both mics.  Point the right one at the left stack, and the left one will then point just outside the left stack.  Keeping them parallel also helps reduce the variables which will make it easier to analyze how well this works afterwards.
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Offline heathen

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Re: Off-center setup/config for specific room
« Reply #39 on: January 21, 2018, 10:39:38 AM »
Reporting back with some results...

For the opening band I did Gutbucket's suggested setup.  We were set up at the sbd, basically straight ahead of the stage left PA.  My mic bar ended up being roughly parallel to the stage, and I aimed my mics at the stage right PA.  They were roughly parallel to each other, about 20 cm apart.  Here is a clip from the opener with that setup: https://drive.google.com/open?id=1bxVLjnm76kdEbzpCyzwKyp5IBPqISvS0

Because there were three of us recording, I decided to experiment even further and changed things up for the main act.  I angled the mic bar so that the right mic was probably at least 4 inches further back than the left mic.  I then aimed the right mic directly at the stage left PA, and aimed the left mic directly at the stage right PA.  Again the mics were about 20 cm apart.  See the attached photo (in case it isn't obvious, my mics are on the bottom).  Here is a clip with that setup: https://drive.google.com/open?id=199FyrOAf99ard43TeToo-2twoslDEJHB

At the show I didn't make any attempt to balance the levels of the channels.  They were linked so they have equal gain.  I also didn't mess with the individual channel levels in post.  The only post done on the above clips was to amplify both channels equally and convert to 16/44.1 flac.

I'd love to hear others' thoughts about how these two setups sound!
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Offline Perry

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Re: Off-center setup/config for specific room
« Reply #40 on: January 21, 2018, 12:17:38 PM »
I like the first sample (Opus 132) better. Just comparing the organ in both tracks- it has a better balance. I've taped from that location at The Other Side a few times- I always end up with too much audience chatter in the left channel. Your technique seemed to help with that problem too. Learning a lot from this thread.
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Offline dmcculh

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Re: Off-center setup/config for specific room
« Reply #41 on: January 21, 2018, 04:47:49 PM »
Both recordings sounded nice, great work.  Listening on headphones: I also liked the opener (first) sample better.  Stereo image seemed a little narrower than the second sample, but I thought it was well-balanced (drums seemed slightly R, bass slightly L, with guitars and keys balanced across).  Second sample did seem to have a wider stereo image to me but it felt weighted slightly to the L if that makes any sense... Thanks for sharing, interested to hear what others have to say.

Offline Gutbucket

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Re: Off-center setup/config for specific room
« Reply #42 on: January 22, 2018, 12:14:32 PM »
Same mic spacing for both sets?

Setup for the first set seems to have worked to balance the off center position for both the band on stage and the audience sounds, yet the resulting recording is overly monophonic for my taste. If using this technique from the same position again, I'd suggest either spacing the mics further apart while keeping them parallel to each other (the simpler answer with regards to technique, though maybe more difficult in practice), or introducing a slight angle between them (trickier to balance, but perhaps easier to arrange).  Good test, thanks for trying it out.

Second set has more stereo interest and is a bit brighter sounding as well, which may be due to a different PA balance rather than the mic setup.  Good test of this technique as well.  This is the Michael Williams technique of positioning one mic forward of the other to use time-of-arrival to help offset level differences to offset the Stereo Recording Angle.  For those following along this is the setup pictured above. Note how the bottom-most rig on the tree has one mic forward of the other- that's the microphone pointing across the stage towards the opposite side PA. 
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