Topic: 3 mic (LCR) distance

[Chanher]

What kind of distances between mics can you guys recommend for a 3 mic mix?

-it will be a LCR (left, center, right) on a stereo bar. (2) Line Audio cm4’s (wide) cardioid on the outside and a single at853 hyper as the center channel.

-I’m really starting to prefer PAS method and I will be doing this with the outside pair. The on-axis response, when pointing your mics forward more, is much more preferable to my ears than leaving the mics pointed outward in a standard ORTF and getting more off-axis sound hitting your capsules. I understand the more you point (directional) mics forward, you need to increase the distance of the mics to maintain stereo qualities.

I have exchanged an email and polite request with Scott from SRS (Shapeways) about taking his swivel ORTF CM4 bar:

https://www.ebay.com/itm/133336035095

and simply making it wider. Then potentially adding a clip dead center to hold the at853 hyper if he can. If he can’t I plan on finagling my own clip.

Knowing this, any recommendations on what the new width should be? If ORTF is 17cm and NOS is 30cm maybe somewhere in the middle at 25cm? Or perhaps just a NOS bar at 30cm? I hope to be running 3 mics most of the time, but in the rare occasion I only run the CM4’s, would 30cm be too far apart for a stereo pair even if they’re wide cardioids and I’m pointing them forward more?

I wish I could experiment myself but I don’t have my cm4’s yet and I wouldn’t mind having my mount ready by the time they arrive. Thanks again in advance for everyone who has indulged my hairbrained ideas as of late, I certainly welcome any critiques of my (probably) flawed logic so far.

[EmRR]

No clear answer.  If you haven't played with the Neumann Recording Tools app or the Shoeps Image Assistant, they'll help visualize what happens with at least the LR pair. 

[Chanher]

No clear answer.  If you haven't played with the Neumann Recording Tools app or the Shoeps Image Assistant, they'll help visualize what happens with at least the LR pair.

oooh very cool, i didn’t know those resources existed. I will check those out after work, thanks.

I know there’s a reference table of some kind that shows the recommended distances with angle change (or something like that)) but I can’t find it and I don’t know if TS search is broken but my search results are off and it doesn’t allow the “3 mic mix” search. I’ll figure it out.

[EmRR]

No clear answer.  If you haven't played with the Neumann Recording Tools app or the Shoeps Image Assistant, they'll help visualize what happens with at least the LR pair.

oooh very cool, i didn’t know those resources existed. I will check those out after work, thanks.

I know there’s a reference table of some kind that shows the recommended distances with angle change (or something like that)) but I can’t find it and I don’t know if TS search is broken but my search results are off and it doesn’t allow the “3 mic mix” search. I’ll figure it out.

http://www.sengpielaudio.com/Visualization-AB60-E.htm

[Gutbucket]

Great question.  The TL;DR is to go as wide as you are able to in practical terms. Two feet is reasonable if you can push the center mic forward somewhat in front of the other two.   The wider you can go the less the center one needs to be pushed forward, which is helpful in multiple ways.


If an extended answer is welcome, read on..

I understand the more you point (directional) mics forward, you need to increase the distance of the mics to maintain stereo qualities.

^
This angle / spacing relationship (in combination with directional pattern) is the core stereo relationship between a stereo pair of mics.. and by extension it applies to arrays of more than two microphones  as well. 

Very generally, a minimum of twice the spacing appropriate for an L/R pair is the starting point for L/C/R triplet spacing.  That kind of makes sense as that makes the distance between any two adjacent microphones the same as it was before.  Problem is the angle between those two adjacent mics is halved, so ideally more spacing is required to compensate for the narrower angle.  The other thing driving the need for increased spacing is the angle between mics that you need to achieve PAS.

I’m really starting to prefer PAS method and I will be doing this with the outside pair. The on-axis response, when pointing your mics forward more, is much more preferable to my ears than leaving the mics pointed outward in a standard ORTF and getting more off-axis sound hitting your capsules.

^
This, in my experience is spot on.  Problem is that from a typical recording position, PAS typically equates to a rather narrow angle between mics, which ideally benefits from increased spacing between them to compensate. Because of that things get wide fast.  Check out the >>Improved PAS table<<, also linked in my signature line.  It's useful as an easy way to determine the optimal spacing between a pair of microphones when Pointed At Stacks, based on the PAS angle from the recording position and mic pattern.  Yet that's two mics, not three.  Three takes more spacing, but it illustrates the trend.

The Neumann Recording Tools app and Schoeps Image Assistant EmRR mentions are useful tools and work for analyzing a stereo pair of mics. These tools are primarily about predicting image width and stereo image position accuracy, which while nice to have is not the most critical thing to a good recording.  But its a good start.  These apps can be a bit wonky and tricky to interpret, so don't feel like mastering or fully understanding them is necessary. The Image Assistant [http://ima.schoeps.de/] is able to analyze a 3-mic array in addition to a stereo pair (not sure about the Neumann app).  To do that it will be easiest to start with the Decca tree preset and modify the mic patterns to emulate those of your mics, then modify mic angle (labeled as Epsilon, equating to half the total angle between L/R mics), horizontal spacing, and center forward spacing to reasonable values while watching the graph display. Read the total image width (the recording angle within which imaging should be accurate) across the bottom, where the diagonal lines curve back to horizontal at lower left and upper right.  Best optimization will form a straight diagonal line running from lower left to upper right across the display, meeting up across the center without too much variation. Play with it and try to get the two diagonals to line up (usually takes adjusting forward spacing as well as L/R spacing). 

Other resources:
I've attached a couple PDFs.  The first covers 3-microphone configurations, except using omnis instead of subcards.  You can use a bit less spacing with subcards in place of the omnis if you angle them.  The second covers 4-microphone configurations using an X/Y or M/S pair in the center in place of the single mic.  Consider doing that if you can.  Page two shows the most compact version, which works in challenging rooms and replaces the omnis with supercardioids.  That can work with subcards too.  Space them a bit more if you can, but don't worry too much if you can't. (These are new revised versions of the old OMT booklet linked in my signature which needs updating)

Michael William's MMAD (Multi Microphone Array Design) website. He's the "Stereo Zoom" author, and much of the stuff above is based on his work. Start here: https://www.mmad.info/MAD/Ch_n_cov.htm.  Similar to the apps, that website all about achieving seamless imaging between microphone pairs, in this case  the multiple mic pairs of an array.  It's a hyperlinked decision matrix which links to printable PDFs showing different microphone array setups.  The 3-mic configuration section was never completed, but the 5 mic section works and starts with the L/C/R front portion, so just choose any configuration angle for the rear-facing mics, and it won't matter if you choose Front Sound Stage Coverage or Surround Sound.  It only uses a single mic pattern for all mic positions however, so choose either cardioid or hypocardioid (subcard).  Then compare choose between approximate PAS angles.  It can be useful to see these known-good arrangements even if you can't achieve them simply as reference points.

[Chanher]

The extended answer is welcome.

I have my homework tonight! It appears my initial idea for an LCR is off, at least in terms of stereo imaging, but I need to read more. I have recorded a couple LCR’s in the last year and I simply enjoyed them, especially the blues trio where I ran the mics onstage. Perhaps this means I need to do some field research and go try more 3 mic mixes with my current gear.

[Chanher]

here is a 1 minute sample of a blues trio i recorded last march in a small theater:

https://www.dropbox.com/s/zb2ajplhisfmlfb/mic%20onstage%20blues%20trio%20sample%202448.flac?dl=0

3 mics LCR onstage, stage lip.
(2) C4 cards ~25cm apart, around 40 degrees
(1) at853rx hyper center

no editing except adding gain to the C4 stereo file (I added a bit more to the right channel to help the mix sound better to my ears).
I did NOT position the center mic forward more (so sound is hitting it first) as I didn't know about the potential benefits at that time. I plan to experiment with this, maybe run it ahead for one set and on an even plane for another.

Is that enough stereo imaging? Yes, for me. But probably because of the onstage setup of the trio. 3 instruments all aligned at the back of the stage about 15-20ft from my mics will do that. You can probably guess the location of the players.

If I'm in a noisy club and I'm pointed at the PA in the back of the room, I question if this setup would make that much more of a difference. The sweet spot up front could potentially catch some stage action. I'll try it out and report my findings.

[Gutbucket]

My work headphones broke yesterday, but will try and give your sample a listen later.  L/C/R works great on stage.  And in that scenario you can often angle the L/R mics wider and push the center mic forward, both of which reduce the need for as much spacing between L/R.

Here's an example of such an on stage setup for a jazz trio-


Based on this MMAD setup-


Similar MMAD setup using cardioids instead of supercards (note the wider angle between mics)

[Gutbucket]

To run a L/C/R without much spacing, ideally the L/R mics should be highly directional and angled widely.  That works up close or on stage, but not so much from a distance.  From an audience recording locations the L/C/R triangle grows increasingly wider and less deep.  That trend continues the farther back the recording position is and as the angle between L&R becomes narrower.  From far back the L/R spread is wide and the forward center spacing minimal.

I've found no better way to deal with a crappy room from an audience position than the "tough room' setup on page 2 of the OMT4 PDF, which uses four channels of directional mics pointed at stacks.

Advantages other than imaging-
I think for tapers the primary advantage of using three mics instead of two is increased flexibility over balance.  It gives you level control over three inputs for L/R balance, center/sides  balance, Left/Center and Right/Center balances.  Much easier to even things out as needed to get a good balanced sound.  Beyond that, the center can be EQ'd differently, which in combination with level control is a super powerful tool.  If open to EQ'ing, try reducing the low frequency content in the center mic channel and EQing higher up for good clarity and presence.  Or try it the opposite way by doing that to the L/R pair.  You can sort of play one off the other to some degree, with lots of options to play around with.  You can do more and push this kind of thing further than you could with a stereo pair because everything gets blended together in a balanced way.

Secondly, the wide spacings or wide mic angles provide a better portrayal of the diffuse reverberent part of the recording - the part that conveys the "sounds like you are there in the room" sensation - while the center mic anchors the middle so there is no hole in the middle problem.

[Chanher]

I think for tapers the primary advantage of using three mics instead of two is increased flexibility over balance.  It gives you level control over three inputs for L/R balance, center/sides  balance, Left/Center and Right/Center balances.  Much easier to even things out as needed to get a good balanced sound.  Beyond that, the center can be EQ'd differently, which in combination with level control is a super powerful tool.

This. There’s an extra channnel on my recorder so why not.

I want to experiment with how far in front I like the center mic. I always assumed having your mics on an even plane in relation to the sound source was a given. Apparently the small time delay difference that comes from moving a centered microphone forward has desireable results. I must test this theory.

[DSatz]

Theory? We don't need no steenkin' theory ...

The three-mike idea comes from the old Bell Labs concept of stereophonic sound in which there would be as many loudspeakers in the playback system as there had been microphones used in the pickup arrangement. When record companies such as Decca, RCA got hold of it for LP recording, home stereo setups were already defined as having two loudspeakers. The center track was thus a utility track, often used for solo elements which could be EQ'ed and balanced (as a whole) in post-production against what the L and R microphones were picking up (as a whole). Think spot miking the soloist in an instrumental concerto or an opera aria--or in a recording of a complete opera, all the singers as a group in relation to the orchestra, where the singers were placed away from the orchestra during the session, so that their closer pickup in the C track would overwhelm their accidental pickup in L and R. This relieved the producer and engineers from having to set those balances during the live session, where they would then become unalterable.

Many Decca recordings had the center microphone placed forward of the line between L and R, but it's a myth that there is one definitive "Decca Tree" geometry; they tried many different arrangements over the years, never settling on any one of them, and often using baffles between/among the microphones to increase the separateness of their pickup from one another. However, in no event did they follow Gutbucket's idea that L and R should be spaced at all widely apart. The entire European conception of spaced-omni miking for stereo is based on a smaller distance between L and R than has ever been traditional in the United States; there are incoherencies in the stereo image (ambiguous / unstable localization of sound sources) that occur with widely-spaced omnis that their ears can't stand (and having learned to hear them myself, neither can I).

RCA, on the other hand, did space their L and R microphones apart more widely, with C deployed either in the true center or else closer to the soloist(s) depending on how the track was intended to be used--as a spot mike, or as a general fill-in. The engineers always ran the center track as hot as possible below the overload limits of the tape, then in the 3->2 mixdown, (a) if C was spot-miked soloists of course the levels were adjusted by ear and from section to section of the music, while (b) if it was a general center fill, then its level was always reduced about 6 dB on average so that it added clarity and anchored the stereo image but didn't collapse everything into mono, as it would do if mixed in at anything like equal gain to L and R.

The Mercury "Living Presence" recordings on the third hand so to speak, if I'm not mistaken, came closer to the idea of three microphones all in a row. The Fines (husband and wife team who recorded the series) didn't always use the same mike for all three positions (actually, six since for safety they ran two separate sets of mikes into two separate three-track recorders), but that was mainly because the mike that they wanted to use for all six positions had already been discontinued before they started recording in stereo, and it was difficult to scrounge up six of them--it took them a few years to do so, but from then on they used that one type of microphone--the Schoeps M 201 in its omni setting--for all their stereo recordings. That's a roughly diffuse-field-equalized pressure transducer with a collar around the diaphragm (apart from when the mike was set to its cardioid position, but they never did that).

Decca and RCA also used microphones with rather special characteristics for these recordings: small-diaphragm pressure transducers (single-diaphragm omnis) where the capsule was embedded in a 40 cm sphere, which gives the microphone added sensitivity in the "presence" region in the front, and causes the on-axis rise in the treble to start at somewhat lower frequencies than it otherwise would for a small diaphragm construction. (The collar around the omni capsule in the Schoeps M 201 had a somewhat similar effect.) Their preferred mike was the Neumann M 50 although both labels also used the M 49 at times--a weird substitution since the capsule construction and sound are quite different. It may have been some situations in which the M 50 wasn't available, or some odd acoustic in some recording venues that required them to use the M 49s as directional microphones, an option which the M 50 didn't offer.

In addition to the three main microphones, Decca and RCA used spot mikes sometimes, and/or "outriggers" (additional, quite widely-spaced L and R microphones whose signals were mixed in to the L and R tape channels at lower levels), but Mercury as far as I'm aware never did so. In all cases there was a separate control room setup with loudspeaker monitors, and test takes were always made at the start of the session, then played back and listened to, so that adjustments could be made before starting the "real" recording.

--best regards

[Gutbucket]

Good historical references, thanks.  Past informs the present.

To clarify, when I suggest the L/R pair of an L/C/R microphone array be "spaced widely apart", that's relative to the "near-spaced" arrangements such as ORTF, NOS, (DIN), etc. concert tapers commonly use.  Relative to the old RCA and Mercury recordings these spacing are not anywhere close to as wide.  The methodology is quite different. 

Backing up a bit- As I see it, the most common problem concert tapers encounter when attempting to introduce additional microphone channels (that is to say, using 3 or four microphones on the same microphone stand, with the intention of mixing them all down to two channel stereo) is placing too many microphones in close proximity / not angled far enough apart from each other to avoid problems.  And this is exactly what I read as being asked about in the original post in this thread.  The well known two-channel near-spaced stereo microphone pair configurations represent optimized combinations of spacing, pattern, and angle.
 Introducing a third channel throws that optimization out of whack and an entirely different combination of spacing, pattern, and angle is required.  Simply adding an additional center microphone channel to a standard two-channel near-spaced stereo pair configuration may seem attractive in practical setup terms, yet is in my opinion not the way to go. 

There are essentially two good choices:
1) Stick with two channels and abandon the idea of using additional microphones.  This is arguably "correct", certainly more simple to implement and is likely the most appropriate choice for most folks.  Use any extra channels for recording the soundboard feed, spot mics.. or to record a second stereo pair arrangement for comparison purposes, choosing one or the other, yet not with the primary intention of mixing them together.

2) Re-arrange things so that a microphone array which includes additional microphone channels it setup to work correctly without problems.  This is what I've been playing around with for years and what I'm attempting to help Chanher with in his exploration of this path.  I've found it engaging and worthwhile for a number of reasons, including the pragmatic aspect of gaining some degree of increased control in situations where tapers otherwise have very little of it, and also in terms of the quality of the resulting recordings when it is done right and it all comes together correctly.

[Gutbucket]

I have played around in the past with wider "in a line" spacings somewhat more similar to what Mercury  "Living Presence" was using, perhaps RCA, some of Owsley Stanley's Old and In the Way recordings, and more recently described by David Griesinger.  Mostly at the stage-lip, using three, four, or five relatively wide-spaced omnis arranged in a line across the front of the stage.  It worked and was fun to do but isn't really practical to do regularly.  Good practical balance control, good resulting recordings, and a fun taper option for some things, yet very different from what most tapers will want to do and what we are discussing here.

A better reference for the spacings I'm suggesting is the more modern 3-channel arrays dating back not 6 decades but more like 2, intended for L/C/R speaker playback (think surround system playback, excluding the surround speakers.. or not).  This is were I initially started with this exploration of recording more than two microphone channels and how best to arrange things for that approach, and I was somewhat surprised and pleased that what worked well for multichannel playback translated extremely well to two-channel stereo playback as well while providing the very welcome increase in practical flexibility mentioned previously.

Am I right or wrong?  Do I care?
The suggestions I'm making here are based on my empirical explorations of this stuff, informed by review of historical methods of recording, the psychoacoustics of human hearing, lots of experimentation and listening, and working within practical constraints of the situations in which tapers find themselves doing our thing.  In doing so I've tried to determine what the underlying core relationships are that seem to be most important, and I try to describe things in those terms on this forum rather than simply saying, "just set things up this way".  It works really well for me, and I'd like to give back to the community by helping other tapers who are interested in exploring recording in similar ways.

That said, my recommendation to most folks remains to stick with two channels!
Fair enough?

[Gutbucket]

Specifically on the thing about forward spacing of the center microphone- Don't worry about it too much. 

Achieving sufficient spacing/angle between adjacent mics is the main thing (something typically near-spaced-like is about right, more as the angle between adjacent microphones grows narrower).  The primary reason for pushing the center mic forward is a way to achieve that if/when you can't otherwise get the L/R pair spaced widely enough, which is to say about twice the spacing of the standard near-spaced two-channel configs). I'd rather have the L/R pair wide enough that the center doesn't need to be forward by much, but having it forward a little bit is good.

^This is not primarily about imaging. Those imaging apps have the center microphone pushed forward to get the image distribution to link up nicely across the center, and playing around with adjusting the forward spacing parameter in them appears to produce major implications.  Don't worry about that too much. Technically accurate source position imaging is nice to achieve, yet is well down on the hierarchy of what is most important.  You'll get plenty of good sounding width and imaging regardless of center-channel forward spacing.

Here's a reasonable practical take on optimizing it- assuming you can achieve sufficient L/R spacing to begin with, push the center microphone forward just enough that the Left-Center microphone pair is perpendicular to an imaginary line pointing at the left edge of the ensemble or left PA stack, and the Center-Right microphone pair is perpendicular to an imaginary line pointing at the right edge of the ensemble or right PA stack.  How far forward that is will be determined by how far back the recording position is.

[fireonshakedwnstreet]

Great discussion, as always. I am typically running an OMT8 with 4ft spread for omnis, but that is with 3 other pairs of directional mics in between them. 2ft should be plenty for two cards and a hyper. The Smallrig 15mm camera rails make a great modular mic bar with the appropriate hardware. Not too obtrusive, light, and sturdy. I have my most directional pair, short shotguns, on a separate bar out front maybe 6 inches or so. I am just trying to get as much direct signal as possible at the show, and I think in that regard the additional directional mics do make a difference. 

[Gutbucket]

^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.

[Chanher]

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.

[Chanher]

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.

[Chanher]

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.

[aaronji]

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"...

[Gutbucket]

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.

[Chanher]

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.

[aaronji]

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).

[Gutbucket]

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.

[Chanher]

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.

[heathen]

I've done some three mic setups, though I don't claim any expertise.

https://archive.org/details/spafford2018-10-27.AT4031.AT853sc
https://archive.org/details/Spyscraper2019-02-02.e614.AT4031
https://archive.org/details/goose2019-02-02.OCT2.e614.AT4031
https://archive.org/details/cycles2018-10-27.AT4031.AT853sc

[fireonshakedwnstreet]

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).

[Gutbucket]

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.

[vantheman]

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.

[Gutbucket]

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.

[Chanher]

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.

I wanted to note an experience this weekend that applies to anyone thinking of adding more mics or currently doing it. I showed up early to a local jazz jam, hoping to get some good 3-4 mic onstage action. Due to multiple circumstances I made the smart decision to ditch all the new gear and just run a simple stereo setup in the sweet spot of the room. Very glad I did. I could just tell the onstage mix would be skewed; they mic'd the quieter instruments through a small PA so out in the room would get the best mix of all instruments and thus the best recording. Ended up with an excellent recording that is very listenable.

My point is don't be afraid to master the art of 2-mic stereo recording as well. I thought of doing 3-mic LCR in the audience, with the center channel picking up some sweet sound direct from the stage, but 2 discrete mics just felt better than a larger 3 mic setup as I was right in front of the majority of the viewing audience. Real-world constraints. I ran at853rx cards PAS straight into the XLR's of the warm mod pmd661 and I couldn't be more pleased.

Side note I'm getting fatigued with the at853 hyper capsules, I think I'm gonna save them for the shittiest of venues and/or extra chatty situations. This is my first time using the warm mod 661 and I think it is just as smooth but more detailed than the mp2. I personally find these mods to be subtle yet still adding pleasing frequency bumps in the right areas. They (usually) make raw files more listenable, skipping tedious post work IMHO. I can't wait to try the CM4's into it.

Also that Schoeps app is VERY cool.

[Gutbucket]

-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.

Saturday I installed smaller Movo windscreens in place of the big Shures in my recording rig for a day of recording Sunday. While doing that I was checking the 3-microphone L/C/R portion of the array against what is suggested by the Schoeps Visual Assistant for this combination of pattern, spacing and angle.  In it, playing around with the center forward spacing mostly affects how correctly the imaging links up between the L/C and C/R segments of the array.  I found that given the pattern, spacing and angle I'm using between the L/R microphones (supercards, 24" [61cm], 45 degrees), Visual Assistant suggests more center forward spacing than the ~6.5" I am using currently.  Alternately or in combination with that, I could push L/R farther apart and/or angle them wider.  Shifting L/R a bit farther apart is what I think I'll do when I rewire everything at some point, as that's when I have the opportunity to adjust wire-lengths and move things around more freely.  The current L/R spacing was originally setup for use with a wider L/R angle, but I found I like the L/R pair more on-axis with the PA so I now angle them +/-45 degrees, and should increase the spacing to compensate for that change in angle.  Ideally I'd like to figure out a way to easily adjust the angle of the L/R pair to anything between, say, +/-30 deg and +/-90 deg when setting up in the field, then adjust spacing to fit the angle.  Would be super slick to build the bar-clamp mechanism in such a way that things are mechanically linked, so the angle would change simultaneously as spacing is adjusted, and all incorrect combinations are automatically avoided, but that's more mechanical complication than necessary.

The only 3-mic arrangements in Visual Assistant that work with no center spacing at all are super-wide arrangements of omnis (typically) in a line. For relatively-narrow arrangements with L/R spacings closer to that of typical 2-channel near-spaced arrangements, the only solution via Visual Assistant is to push the center microphone position much farther forward, something like 1 to 2 meters or more (in plan view the LCR triangle becomes very tall with a narrow base, rather than wide at the base with relatively minimal height), which then requires the application of delay or manual time-position shifting of the center signal in the DAW such that an impulse from the stage is time-aligned across all three channels.  That's not a practical taper arrangement at all though, as front back spacing is usually more difficult to achieve in taper situations than left/right spacing.

As mentioned earlier in this or in another thread, if free to adjust pattern, spacing and angle, the sweet spot for tapers with regard to forward spacing of the center microphone position might be to use whatever arrangement achieves good image linking while placing the baseline of the L/C pair perpendicular to a line to the left PA stack,  and vice-versa for the C/R pair and the right PA stack.  Sort of PAS with regard to the each baseline on either side of center.  That should optimize imaging as well as transient arrival from each stack to each side.  It will also tend to produce a triangle arrangement that is significantly wider at the base (L/R) with relatively minimal forward spacing of the center.

[Chanher]

My very crude visual depiction of gutbuckets “triangle” explanation of how to place the forward Center mic in an 3-mic LCR arrangement. As I understand it, you want to make an imaginary triangle (math people plz tell us the type of triangle) with the Left mic, Center mic, and left PA speaker, and then a second triangle with the Right mic, Center mic, and right PA speaker. I plan on trying this the next chance I get.

Please correct or add anything.

[Gutbucket]

Yes, that's what I'm proposing as a reasonable, relatively easy to apply rule of thumb that aims to get time-alignment right natively without needing to do anything in the DAW, while also achieving about the right forward-center spacing needed for good image linking.

[Gutbucket]

Below is a screen-shot of the L/C/R microphone arrangement currently comprising the center portion of in my rig, simulated in Image Assistant after measuring it up last weekend.  The angle of the L/R microphones in the rig are currently constrained to +/-45 degrees.  From the Image Assistant curves it appears this arrangement would benefit from a bit more center forward spacing so as to achieve optimal image linking.

So in the second image, I've shifted the center mic 5cm farther forward, which visually improves linking in the graph, but also widens the SRA a slightly by doing so.

BTW, it sounds good as is, without using any time alignment - and the forward spacing is pretty close to achieving the geometric alignment Chanher and I discuss above.