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Author Topic: 3 mic (LCR) distance  (Read 1965 times)

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Offline Gutbucket

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Re: 3 mic (LCR) distance
« Reply #15 on: October 21, 2022, 01:33:44 PM »
^You're fully into the optimized multichannel thing.. exploring the logical extreme of the thing much as I do.  I hesitate to suggest most folks go that far.  Its fun though!

One more general thought-
Like most things, the key is gravitating to the "just right" mid-point between extremes.  Not too much spacing or angle, yet also not too little.  Not too many channels, but neither too few.

The multi-microphone array I recommend to most folks wanting to try using more than two microphones in combination is four channels total: a coincident center pair placed in between a "mid"-spaced pair using spacing twice as wide as a typical near-spaced pair used on its own.  That represents a practical, not overly complex arrangement not difficult for tapers to achieve.  The better it sounds in the room at the recording position, the more open of a pickup pattern can be used in the twice-near spaced pair.  And the more open the pair the wider it should be.  Not that complicated.

The coincident pair does a nice job with imaging and center solidarity that might otherwise be weak in the twice-wide pair.  The twice-wide pair does a nice job providing an open ambient feel a coincident pair often tends to lack.  Because both in combination serve to cover the weaknesses of the other, each of them need not be as perfectly configured as they otherwise would need to be when used on their own in isolation.

Same guidelines for spacing as the 3-microphone configurations discussed above, but the coincident pair in the center instead of a single microphone is a big advantage in my experience.  For those suspicious of arrays of more than 2 microphones, this is what I'd suggest trying. It works really well in practical terms for concert taper scenarios.  Try it and see if you like it.  It's perfectly okay not to like it, but try it first in a few taper scenarios, give mixing the two pairs a bit of listening effort, and then decide if its something you like and worthwhile or not.
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Offline Chanher

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Re: 3 mic (LCR) distance
« Reply #16 on: October 23, 2022, 03:42:21 PM »
A lot of excellent information and history in this thread, thanks guys.

My preferred approach is to take in as much info and theory as you can, then throw it out the window and go tape. set up however you want. If you keep taping and learning you'll have good results.

I'm planning a low-profile homemade 3 mic bar in my head, will post pics.
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Offline Chanher

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SAMPLES: 3 mic (LCR) distance
« Reply #17 on: November 27, 2022, 02:23:37 PM »
I recorded Fleece, a fun 4 piece from Montreal the other week and the stars aligned for a 3 mic LCR in the "sweet spot" + mono soundboard. I thought I'd share some samples so everyone can hear and compare a stereo pair, a 3 mic mix, and a 3 mic mix + a soundboard feed.

This was at Lost Lake in Denver and it is a smaller dive venue. The room is a bit odd as it's more wide than long, BUT that means the "sweet spot" is much more accessible as it is literally right where the soundboard is (slightly LOC but only 25-30 ft from the stage/PA). Chris the soundguy let me put my mic stand up on the actual table (legs closed) and taped to the corner which pretty much puts it pretty much DFC. Perfect spot.

CM4's are ~28cm apart at ~40 degrees and I ran them into the MP2
C4 hyper as center mic (bass roll off switch engaged), about an inch ahead of the CM4's. Straight into the dr70d

I have 4 different samples:

01 stereo CM4 pair (normalized)
02 mono C4 hyper with bass roll off switch engaged (normalized)
03 3 mic LCR with some slight EQing and normalized
04 3 mic LCR mix + mono soundboard mastered, EQ'd, and normalized

https://www.dropbox.com/scl/fo/akf2ez14mg7vthk1fdfv5/h?dl=0&rlkey=6zctnokzb1aylf65qv3g8potm

Sorry for the crappy pics, my phone's camera is all screwed up and it took me forever to just to get these crappy pics. All my money has gone to gear so no new phone haha.
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Offline Chanher

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SAMPLES: 3 mic (LCR) distance
« Reply #18 on: November 27, 2022, 02:53:31 PM »
some notes:

-I didn't put a sample of the mono soundboard feed, if anyone wants to hear that lmk. I was expecting the usual vocal-heavy mix, but it was actually very keyboard heavy. I did my best to even it out with compression and EQ but I'm still somewhat inexperienced with these tools. As many of you know, mixing in uneven soundboard feeds is a little dangerous; it very often has a negative effect on the actual MIX of the instruments. We naturally want to improve our recordings and the clarity of a soundboard feed technically does that but at what cost? If it upsets the balance of instruments and vocals (some instruments suddenly are clear and upfront while the others are distant and quieter) is that actually improving the recording? I'm still undecided if the sample with the sbd is listenable as I do feel the keyboard is a bit louder than the other instruments. Opinions and critiques are welcome.

-I should definitely mention that even though I had the center mono hyper ~1 inch AHEAD of the CM4's (as recommended), I ended up visually lining up snare hits on ALL sources/feeds. I did some quick listening to the 3 mic mix with the center mic left alone and then with it visually aligned (the actual difference was miniscule) and if I'm being honest I didn't hear any difference so I left it lined up. I know Gutbucket talked about moving the center mic forward more in relation to the distance of the outside (left right) stereo pair and perhaps in future recordings I can experiment with that.
« Last Edit: November 27, 2022, 07:32:07 PM by Chanher »
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Re: SAMPLES: 3 mic (LCR) distance
« Reply #19 on: November 29, 2022, 04:33:02 PM »
I did some quick listening to the 3 mic mix with the center mic left alone and then with it visually aligned (the actual difference was miniscule) and if I'm being honest I didn't hear any difference so I left it lined up.

Sound moves about one foot per millisecond (it varies a bit due to a bunch of factors). So one inch is only a twelfth of a millisecond. Reports vary, but that is still below the lowest estimate of audibility that I recall seeing. I would be very surprised if you could hear that. I would still line them up, though, if for no other reason than "because why not"...

Offline Gutbucket

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Re: 3 mic (LCR) distance
« Reply #20 on: November 30, 2022, 12:17:48 PM »
Thanks for the samples, I'll try and give them a listen maybe tonight or this weekend.

I don't expect the exact forward spacing of the center mic to be super-critical here, and it looks like a reasonable arrangement in your photos. In general, use a bit of forward spacing for the center microphone and don't worry too much about it.  In one sense it may be advantageous to arrange things so the Left/Center mic pair is perpendicular to an imaginary line pointing at the left PA speaker and the Center/Right mic pair is perpendicular to an imaginary line pointing at the right PA speaker, which is easy enough to visualize and apply at setup.

May not be necessary, but if you'd like to play with slight modifications to this arrangement the next time out, I'd try increasing the spacing between Left and Right microphones when the center mic is in play.  One way to know when such a 3-microphone arrangement is close to optimized is when the Left/Right pair sounds a bit over-wide or a weak across the center when listened to in isolation with the center channel muted, but the 3-channel mix is well balanced with the center channel unmuted.   That's not critical to making a good recording which benefits from the center microphone, but will tend to make the best of the combination of the 3-microphones.


More technically-
In terms of imaging, forward spacing of the center microphone is mostly relevant when playing back the 3 recorded channels discretely over 3 speakers across the front, in regards to getting a precisely accurate image distribution across the boundary between the left-center speaker sector and the center-right sector.

In terms of achieving a low value of diffuse field correlation (which is what makes the ambiance and reverberation in a recording sound natural, open and enveloping) significantly greater spacing is required (a few feet, rather than a few inches), which when applied to how far forward the center microphone position would likely require application of delay or visual alignment to bring the direct-arriving sound from the stage and PA back into proper coherence across all three channels.  Increasing spacing between the Left and Right microphones won't require additional delay or visual alignment to keep the sound arriving from the stage/PO coherent while likewise decreasing diffuse field correlation, and even a slight increase helps achieve better diffuse decorrelation, up until it gets too wide such that the center microphone starts sounding more like a separate island of sound and the good smooth, solid image distribution between speakers begins to suffer.
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Offline Chanher

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Re: SAMPLES: 3 mic (LCR) distance
« Reply #21 on: November 30, 2022, 04:29:05 PM »
I would still line them up, though, if for no other reason than "because why not"...

I gotta line em up. Gutbucket is right, I shouldn't worry about it too much, but I can't help it.

I'd try increasing the spacing between Left and Right microphones when the center mic is in play.  One way to know when such a 3-microphone arrangement is close to optimized is when the Left/Right pair sounds a bit over-wide or a weak across the center when listened to in isolation with the center channel muted, but the 3-channel mix is well balanced with the center channel unmuted.   That's not critical to making a good recording which benefits from the center microphone, but will tend to make the best of the combination of the 3-microphones.

Yes, I was limited by that particular stereo bar. But I'm sooo close to finishing the final version of my homemade adjustable stereo bar that will allow widths up to 47cm for the outer pair. I used an early prototype for a 3-mic trial recording last month with the cm4's at 47cm and at that width the cm4's by themselves are (obviously) much too far apart. But when I added the at853 hyper to the mix it was much more balanced and full. Even for a 3 mic mix my initial impression is that 47cm (for the outer pair) is a bit too far, fortunately I'll be able to play around with that width and I'll probably try around 40cm's when the bar is completed. That room (and mix) sounded like shit so I didn't wanna put the time into mixing and mastering that particular recording.

I've been thinking about setting up a video camera right behind my mics at a show and slowly (and smoothly) sliding the outer mics to different widths and angles WHILE recording a band. Then line up the audio with the video in post and we'll be able to HEAR how different widths and angles affect the sound while watching the mics being moved. I'm a visual learner and for some reason this kind of experiment really appeals to me. I need to finish my stereo bar first and then find a show in a decent sounding room where I have the flexibility to pull this off, the stand can't be raised really high unless I wanna bring a ladder (not happening).

You mentioned previously in this thread that a 4-mic mix is actually the best sounding option for anyone wanting to go beyond 2-mic stereo recordings and I agree; I'm just limited by my 4-track DR70d and I tend to have the option of a mono sbd feed at a lot of shows I tape. It just seemed logical to me to try to use the 3 available channels (after getting a mono sbd feed) in the form of a LCR 3-mic mix. Hopefully these experiments and samples demonstrate just how beneficial the 3rd mic can be, I'm certainly open to the possibility that it's not worth the effort. It's definitely a lot of fun trying it out though! When I have some shows with no sbd option I'm excited to try (2) at853 hypers in XY between either some omni's or the CM4 wide cardiods.

These Tascam DR70d's are going so cheap now and IMO the current firmware is stable and reliable. I'd sure love to upgrade to the new Mixpre's/Zoom's but I plan on keeping this for awhile as I only paid $179 on ebay and the Mlady batteries on Amazon are $22 for a 2 pack and 1 of those will power the DR70d for 10+ hours. For around $200 you have a 4 track recording setup, unheard of in the early 2000's when I started experimenting with aud + sbd matrices. Side note someone buy Dan's Mixpre 3ii in the yardsale before I do haha.
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Re: SAMPLES: 3 mic (LCR) distance
« Reply #22 on: November 30, 2022, 05:30:47 PM »
I would still line them up, though, if for no other reason than "because why not"...

I gotta line em up. Gutbucket is right, I shouldn't worry about it too much, but I can't help it.

I am right there with you! It isn't hard to do and it would nag at me if I didn't align them (even if I couldn't hear a difference).

Offline Gutbucket

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Re: 3 mic (LCR) distance
« Reply #23 on: November 30, 2022, 05:42:09 PM »
Note on lining up the waveforms in the DAW- Don't get flustered when aligning files from a non-coincident microphone configuration only to find that some of the peaks line up perfectly while others don't.  Only sound sources located directly in front and behind the array should line up exactly.  Any source located over to the left or right will naturally be somewhat misaligned as the wavefront will reach one microphone slightly before the other, more so the farther off to one side or the other the source is and the wider the spacing between microphones.  By contrast, with coincident microphone arrays all peaks and valleys should line up regardless of source position.  Extra credit for anyone pointing out the special case detail with certain coincident arrays.

The idea of videoing the setup while adjusting the spacing is brilliant.  You can really get a good feel for dialing it in, for how much things change and by how much, by doing it that way.  Just keep in mind that you are likely to end up with different spacing preferences depending on things like how far away the recording position is and what angle you are using between the left/right pair.

I did something similar when playing around with the spacing between omnis years ago, but did so by writing down the spacings and the recording time-point for each change on a note-pad.  Lots of scribbling.  Videoing it sounds much easier.  If not too much hassle, share the video here.  I'd love to check it out and bet others would too.

To clarify, I think 4-mic arrays using a coincident center pair (which is still only 3 LCR microphone positions in space) represents a good/reasonable sweet spot for most tapers wanting to play around with using more than two microphone channels.  Best sounding might be just two channels.. or six, or whatever.  Too many variables to predict best sounding, and a lot of it is how you set things up and how you use whatever you've got.  Mostly I think using more than two microphone channels can help to stack the deck in your favor, making it more likely you can produce a great sounding recording given all the real-world constraints under which tapers record.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Chanher

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Re: 3 mic (LCR) distance
« Reply #24 on: November 30, 2022, 07:02:14 PM »
Note on lining up the waveforms in the DAW- Don't get flustered when aligning files from a non-coincident microphone configuration only to find that some of the peaks line up perfectly while others don't.  Only sound sources located directly in front and behind the array should line up exactly.  Any source located over to the left or right will naturally be somewhat misaligned as the wavefront will reach one microphone slightly before the other, more so the farther off to one side or the other the source is and the wider the spacing between microphones.  By contrast, with coincident microphone arrays all peaks and valleys should line up regardless of source position.  Extra credit for anyone pointing out the special case detail with certain coincident arrays.

The idea of videoing the setup while adjusting the spacing is brilliant.  You can really get a good feel for dialing it in, for how much things change and by how much, by doing it that way.  Just keep in mind that you are likely to end up with different spacing preferences depending on things like how far away the recording position is and what angle you are using between the left/right pair.

I did something similar when playing around with the spacing between omnis years ago, but did so by writing down the spacings and the recording time-point for each change on a note-pad.  Lots of scribbling.  Videoing it sounds much easier.  If not too much hassle, share the video here.  I'd love to check it out and bet others would too.

To clarify, I think 4-mic arrays using a coincident center pair (which is still only 3 LCR microphone positions in space) represents a good/reasonable sweet spot for most tapers wanting to play around with using more than two microphone channels.  Best sounding might be just two channels.. or six, or whatever.  Too many variables to predict best sounding, and a lot of it is how you set things up and how you use whatever you've got.  Mostly I think using more than two microphone channels can help to stack the deck in your favor, making it more likely you can produce a great sounding recording given all the real-world constraints under which tapers record.

Once again you are correct, peaks may not line up within a stereo file as the sounds (from the sides) are hitting the mics at (slightly) different time intervals. that's what creates stereo sound! how quickly I forget, perhaps I'll leave the center track alone.

I shouldn't have used "best sounding" when describing 4mic vs 3mic. Describing 4mics (with 2 coincident mics in the center) as the "sweet spot" when experimenting with more-than-2-mics is a good way of putting it.

It might be a while before I can get to the video experiment but hopefully sooner than later and I'll certainly post the results here. Thanks again for the guidance.
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Offline fireonshakedwnstreet

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Re: 3 mic (LCR) distance
« Reply #26 on: December 01, 2022, 05:48:03 PM »
Agree DR-70D is a great box for the money. If you want to expand on a budget the DR-680 (mki or ii) can be had for cheap and you can get up to 8 channels (with digi-in).
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Offline Gutbucket

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Re: 3 mic (LCR) distance
« Reply #27 on: December 09, 2022, 05:13:31 PM »
Following up on this discussion..
Here's a link to the Schoeps image assistant (available in on-line version and phone app) capable of assessing 3-microphone setups in addition to 2-channel ones, which allows for choosing a different pickup pattern for the center microphone position, and can be fun and informative to play around with- https://schoeps.de/en/knowledge/image-assistant.html

I thought this was posted early in the thread but it appears not.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline vantheman

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Re: 3 mic (LCR) distance
« Reply #28 on: December 10, 2022, 02:23:28 PM »
This app looks great. I could have used this just a week ago. But what does the Epsilon value mean here? It doesn’t seem to alter the visualization at all.
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Offline Gutbucket

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Re: 3 mic (LCR) distance
« Reply #29 on: December 10, 2022, 03:08:15 PM »
It's the angle of the L/R mics, measured as half of the total angle between them (90 degrees = fully side facing, 180 degrees apart).

If altering its value does nothing, its likely that mk2 omnis are selected for both the left and right microphone positions, which I think is the default.  Switch them to a directional pattern and you'll see any changes in Epsilon reflected in both the top-down view of the array in the upper left and the visualization curves.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

 

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