Topic: recording acoustic musicians sitting in a circle

[cybergaloot]

I may have asked this before but don't remember any answers that stuck with me. I have friends who have an annual "pickin' party" where people basically sit in a circle and play. Here's what it looks like: https://www.youtube.com/watch?v=xvTnOsGA2nI How would you mic that? I have an LSD2 and thought about setting it to dual figure-8 patterns (Blumlien basically) and just setting it in the middle about 3-4 feet up.  I think the stereo image would be distorted (musicians sitting across from each other would sound like they were side by side) but without an ambisonic mic and a surround playback system I don't t see any way around that. I'm thinking that maybe a second set of cardioid mics on a stand about 7-8 feet tall split a couple of feet, aimed down and somewhat away from each other might help fill out the sound but not the imaging problem. 

Another thought would be to just set up a paid of mics on a stand just outside the circle aimed at the center.

Any thoughts of a better method?

[bryonsos]

Why not use an omni or two?

[cybergaloot]

I wondered about a split omni set up. The LSD2 figure-8 idea is basically omni with a bit of stereo separation. That has the advantage of using just one mic although it is a big brute.

I don't know when or if I'll get a chance to test this. That pickin' party is 200 miles west of me and I'm usually working 100 miles east of here on that weekend but I'd sure like to catch it one day. Its just that the set up issue has always bothered me.

[Bruce Watson]

I'm thinking that maybe a second set of cardioid mics on a stand about 7-8 feet tall split a couple of feet, aimed down and somewhat away from each other might help fill out the sound but not the imaging problem.

I'm thinking a set of omnis in AB30, on a stand about 7-8 feet tall, aimed straight down. Nothing you can do about the imaging problem, for stereo you have to reduce that circle down to a line (between the speakers) no matter what you do.

[cybergaloot]

Yep, surround would be the only way I can see to fix the imaging but it would be like you were sitting in the center of the circle, something most of us would never do. Mics on a stand outside the circle would be more like what  a listener there would hear. The problem with that the volume levels between the instruments would be a bit out of kilter. The closer or more directional instruments might be overly loud and the ones to one side might be quieter. Split mics in the center of the circle might have phase issues but I do not know that for sure since I haven't tried it.

Most of the time we record situations with the audience on one side of a line and the musicians on the other. The circle throws in a kink. Now that I think about it I sort of tried it once before but in that case it was a large circle  of people around a campfire but the musicians were clustered in one arc of the circle. I couldn't get between the fire and musicians so I set up on the other side of the fire. The results were not so good. lots of fire crackling with music in the background.

[voltronic]

Interesting problem.  Personally, I'd go with the center of the circle sound to capture all the players equally.  You won't get the front-to-back imaging unless you go with a surround setup, but one of these could get you a good stereo image without phase problems, using just two mics:

- Omnis on a jecklin disc
- Omnis on a dummy head
- PZMs mounted back-to-back on either side of a plexiglass sheet
- narrow spaced omnis as Bruce suggested

I'm not sure I'd go with any of these mounted on very tall stands, because then I feel you would lose some of your stereo separation created by the boundaries / spacing between the mics.  You don't want the recording to sound like someone standing on top of a tall ladder above your circle.

[cybergaloot]

I hadn't thought of using a jecklin disc. Interesting!

[Gutbucket]

Jecklin works great for this in  the center of the circle right at shoulder level.  Gets everyone equally all around the circle with really nice imaging.  Slightly spaced 180 degree omnis work without the baffle too, it's just more nicely defined with the baffle.  Down low like that gets it nice & intimate sounding and the players bodies really help block noise from talkers outside the circle.  If it's not a cocktail chat scene outside the circle and there is a second orbit with additional players or people singling along you'd like to pick up more of, then you can go high with a more typical near-spaced config pointed directly down into the center of the circle.  If one player is the obvious anchor, you might tilt that their way a bit.  If you need to use cardioids down low at shoulder level I'd arrange those 180 degrees coincdent, but omnis will probably work beter.

[F.O.Bean]

I would do something like what Schoeps sells and do a double ORTF or something like that! Its just one pair of mics facing forward, and one pair of mics facing backwards. Then you could just sync them up and do a matrix in post. Should sound pretty cool too. Its just a 4 channel surround setup without an ambisonic mic

[cybergaloot]

I guess I need to make myself a Jecklin disk sometime. I don't if or when I'll ever make it over to the pickin' party I'm thinking about but those boys can play! If you know who Guthrie Trapp is, he is basically a former protege of theirs.

[weroflu]

blumlein renders sort of surround sound somehow with only two mics, not sure how it does it but it does it.

[cybergaloot]

blumlein renders sort of surround sound somehow with only two mics, not sure how it does it but it does it.

http://en.wikipedia.org/wiki/Blumlein_Pair

Blumlein is essentially four coincident omni mics but two with flipped polarity.

[cybergaloot]

blumlein renders sort of surround sound somehow with only two mics, not sure how it does it but it does it.

http://en.wikipedia.org/wiki/Blumlein_Pair

Blumlein is essentially four coincident omni mics but two with flipped polarity.

Here's a really good video of how they get the various mic patterns but I don't remember if it included Blumlein: https://www.youtube.com/watch?v=ihAG6cMpUlY&list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw

[Gutbucket]

I guess I need to make myself a Jecklin disk sometime. I don't if or when I'll ever make it over to the pickin' party I'm thinking about but those boys can play! If you know who Guthrie Trapp is, he is basically a former protege of theirs.

You can make due pretty well by just setting up two omnis at shoulder height, spaced about a foot apart or so on a mic bar, then draping a jacket or sweater or something over the bar between the mics.  Might help to mount the mics upside-down on the bar so they hang beneath it, so the draped jacket or whatever is high enough to properly baffle them.  As long as whatever you put between the mics effectively blocks the sound from arriving from the opposite side, yet both mics can still 'see' the performers to the front and back of the plane between the mics it's good.   It's also somewhat casual and less imposing than a fancy disk, which might make the performers more relaxed.  I like shoulder or chest height because it is about equidistant to both the voices and instruments, so both are clear and close and neither is over represented, and it's low enough that the performers can easily see each other over the top.  That's far less imposing than something at head height blocking the view and potentially killing the vibe, or even up high looking down on things.

[Gutbucket]

I would do something like what Schoeps sells and do a double ORTF or something like that! Its just one pair of mics facing forward, and one pair of mics facing backwards. Then you could just sync them up and do a matrix in post. Should sound pretty cool too.

A common setup for recording four channel ambient surround atmosphere material is the IRT cross, which is simply four cardioids (or supercards using less spacing between mics) arranged in a cross shape pointing outwards.  http://www.schoeps.de/en/products/categories/irt-cross

If mixing those four channels down to 2-channel stereo, you have two basic choices.  I'd play with routing them both way and go with whatever sounds best.  Looking at the cross from above and going around the circle  of microphone channels you could route the four mics either:

Left, Left, Right, Right
-or-
Left, Right, Left, Right

The first would provide imaging somewhat more like Jecklin baffled omnis- the players on one half of the circle would image Left, and the other half would image right.  Because of the cross-talk between adjacent mics on each side getting mixed together, listen for potential comb filtering problems.

The second way would image somewhat more like Blumlien, with quadrants of the circle imaging Left/Right, Right/Left, Left/Right, etc.. all the way around. The difference is there would be no reverse polarity quadrants as with Bulmlien.  I suspect the second way would work best, but you never know until you actually try it.

[Edit- fixed link. The IRT cross is symmetrical and doesn't favor any particular direction which may be most appropriate in the center of the circle.  Double ORTF is similar, and could be mixed similarly, but isn't symmetrical and wouldn't have as symmetrical a playback image of all the musicians arranged in a circle.  It's meant more as a forward/backwards oriented surround recording setup- basically a surround extension of typical forward facing ORTF stereo)

[Gutbucket]

Following up on that-

If you had no spacing between those four IRT-cross cardioids, matrixed them the second way and flipped polarity of the two on one side of the circle, you'd essentially have a Blumlien arrangement.

If you think about the Stereo Zoom implications and consider the spacing between the four cardioid microphones in an IRT configuration, it may be apparent why I suggested a coincident arrangement if using only using two cardioids facing 180 degrees apart. 

[cybergaloot]

I guess I need to make myself a Jecklin disk sometime. I don't if or when I'll ever make it over to the pickin' party I'm thinking about but those boys can play! If you know who Guthrie Trapp is, he is basically a former protege of theirs.

You can make due pretty well by just setting up two omnis at shoulder height, spaced about a foot apart or so on a mic bar, then draping a jacket or sweater or something over the bar between the mics.  Might help to mount the mics upside-down on the bar so they hang beneath it, so the draped jacket or whatever is high enough to properly baffle them.  As long as whatever you put between the mics effectively blocks the sound from arriving from the opposite side, yet both mics can still 'see' the performers to the front and back of the plane between the mics it's good.   It's also somewhat casual and less imposing than a fancy disk, which might make the performers more relaxed.  I like shoulder or chest height because it is about equidistant to both the voices and instruments, so both are clear and close and neither is over represented, and it's low enough that the performers can easily see each other over the top.  That's far less imposing than something at head height blocking the view and potentially killing the vibe, or even up high looking down on things.

Then I'd worry that people would think it was the coat rack!    I don't have a disk and have never played with one so it might be fun to make one. I've got some plywood, foam and dead rat fabric so it wouldn't cost me anything. I think I even have all the mounting hardware I'd need.

I have thought about not wanting the setup to be a distraction for either the musicians or the other listeners. It's not about me, its all about them!

[Gutbucket]

I have thought about not wanting the setup to be a distraction for either the musicians or the other listeners. It's not about me, its all about them!

You know it.  And unfortunately that's the potential issue with any baffle, they can be an imposing distraction.

I once used a small pizza box as a makeshift baffle, stuffed with a couple old dirty t-shirts inside.  Might have made a more tempting target than a coat rack, but would have been an surprise to anyone searching for a bite!

[capnhook]

OK I will ask the dumb question...... ......why not blumlein in the center?  You got a LSD2............

[cybergaloot]

OK I will ask the dumb question...... ......why not blumlein in the center?  You got a LSD2............

That was actually one of the original considerations. You need to come visit sometime Kevin!

[capnhook]

OK I will ask the dumb question...... ......why not blumlein in the center?  You got a LSD2............

That was actually one of the original considerations. You need to come visit sometime Kevin!

Ok, then we can really cover some ground...........lets put 2 LDS2's in the center!

Those pickers are really good, Walter..

[Gutbucket]

Blumlein might work nicely, but the two side quadrants are out of polarity so performers in those sections of the circle may image oddly and suffer from weak bass response.  Would be best to arrange things so players of importance, including the bass player, are within the front and rear quadrants if possible, and the sing-along egg-shaking hangers on and second-liner's are in those side quadrants.

If you play that back through a home theater setup and turn on the Dolby/DTS/Logic7/THX matrix surround mode in the receiver, the sources in those side quadrants will be what gets wrapped around to the surround channels in back half of the room.  The sources in the quadrants directly in front and behind the microphone will image between the front speakers.

[cybergaloot]

Those pickers are really good, Walter..

The guy singing and playing mandolin was a roommate for a while back in the middle 70's and the guy playing bass (also a killer guitar player) is a friend from high school. They just aren't much interested in having a touring band.

[Gutbucket]

I'll have to check out that Youtube link when i get home.

You guys may remember this thing from my oddball thread.. One of the first things I built when I started hanging out around here at TS years ago-  A two omni boundary-mounted hemispherical baffle contraption designed to be set on the ground in the middle of a circle of pickers.  It worked pretty well, but would have worked even better if it was higher up off the ground and provided a bit more baffling between the two channels.  In a few recordings it seemed to really emphasize circadias up in the trees directly above the circle.

I made it before going to a week-long guitar camp.  The baffle housed an R-09 recorder and MMA6000 preamp to form a quick portable an all-in-one recording thingamajobber.  Or take out the recorder and preamp to operate them remotely and insert the foam blocks for a full half-sphere baffle (I never actually used it that way).

[voltronic]

I guess I need to make myself a Jecklin disk sometime. I don't if or when I'll ever make it over to the pickin' party I'm thinking about but those boys can play! If you know who Guthrie Trapp is, he is basically a former protege of theirs.

You can make due pretty well by just setting up two omnis at shoulder height, spaced about a foot apart or so on a mic bar, then draping a jacket or sweater or something over the bar between the mics.  Might help to mount the mics upside-down on the bar so they hang beneath it, so the draped jacket or whatever is high enough to properly baffle them.  As long as whatever you put between the mics effectively blocks the sound from arriving from the opposite side, yet both mics can still 'see' the performers to the front and back of the plane between the mics it's good.   It's also somewhat casual and less imposing than a fancy disk, which might make the performers more relaxed.  I like shoulder or chest height because it is about equidistant to both the voices and instruments, so both are clear and close and neither is over represented, and it's low enough that the performers can easily see each other over the top.  That's far less imposing than something at head height blocking the view and potentially killing the vibe, or even up high looking down on things.

I've also used a towel draped over a vertical music stand, same idea.

[cybergaloot]

You've always come up with some interesting rigs. I remember when I met you that you had a painter's pole stuck in your folding chair with, I think, antennas sticking out with the DPAs at the end. I love it when I'm at the SOSMP and see that curent rig of yours pop up in the middle of the crowd. AAA+++ for inventiveness!

[Tom McCreadie]

I'd go with a Jecklin Disk. You could cobble up a quick 'n dirty JD by glueing a stack of old LP's - I urge you to use up any Barry Manilow's, for optimum sound  :-) - and covering that stack with some rubber carpet underlay or maybe a few old pc mouse mats.

With performers evenly around a circle, the Blumlein array does have two disadvantages:
1. Sounds from the two extreme L and R sectors fall in the "ambiophonic" region. That is, they deliver opposite polarity voltages to the two coincident mics (one mic getting a +ve signal while the other mic gets a -ve value). This results in a woozy, vague imaging of those sound sources.

2. Sounds from the rear sector will - besides generating signals of a polarity inverse to those from the front - also give a 'laterally-inverted' imaging, e.g. sources  located at, say, "4-o'clock" and "5-o'clock" will image as if they had been located at 8- and 7-o'clock, respectively. 

To illustrate this further, a consequence would be that, for a perfectly-centred array and 6 performers A...F stationed at direction angles of  A 10-30, B 11-30, C 12-30, D 1-30, E 5- and F 7-o'clock, the resultant imaging from a two-speaker playback would likely be in the following sequence:
- from Jecklin Disk:        L  ->     A - F - B - C - E - D     ->   R
- but from Blumlein:      L ->      A - E - B - C - F - D     ->   R

[cybergaloot]

I figured the stereo imaging would be weird but I didn't take into account the inversion of the rear sources. And I definitely didn't consider the "ambiophonic" region. That sounds like a game killer to me. Time to make a disk and try testing it some. I think there is a pickers group that meets periodically here in Tallahassee. I'll have to figure out where they meet.

[voltronic]

I'd go with a Jecklin Disk. You could cobble up a quick 'n dirty JD by glueing a stack of old LP's - I urge you to use up any Barry Manilow's, for optimum sound  :-) - and covering that stack with some rubber carpet underlay or maybe a few old pc mouse mats.

With performers evenly around a circle, the Blumlein array does have two disadvantages:
1. Sounds from the two extreme L and R sectors fall in the "ambiophonic" region. That is, they deliver opposite polarity voltages to the two coincident mics (one mic getting a +ve signal while the other mic gets a -ve value). This results in a woozy, vague imaging of those sound sources.

2. Sounds from the rear sector will - besides generating signals of a polarity inverse to those from the front - also give a 'laterally-inverted' imaging, e.g. sources  located at, say, "4-o'clock" and "5-o'clock" will image as if they had been located at 8- and 7-o'clock, respectively. 

To illustrate this further, a consequence would be that, for a perfectly-centred array and 6 performers A...F stationed at direction angles of  A 10-30, B 11-30, C 12-30, D 1-30, E 5- and F 7-o'clock, the resultant imaging from a two-speaker playback would likely be in the following sequence:
- from Jecklin Disk:        L  ->     A - F - B - C - E - D     ->   R
- but from Blumlein:      L ->      A - E - B - C - F - D     ->   R

Every time I've heard a Blumlein recording of singers in an arc around the array, I've always thought it sounded very unrealistic compared to ORTF cards or spaced omnis in the same space.  I wonder if the effect you're describing partially accounts for this.  Maybe this is not a mic setup that is good to use close up when you have sound coming from multiple directions.

[Gutbucket]

Blumlien works best when you only have ambient room sound stuff (reflections, reverb, applause, maybe ambient wash stuff, and whatever) in the side quadrants.  That stuff really works well when located there and is part of what makes Blumlein so magical sounding. The inverse polarity (of both channels equally) and mirror flipped imaging in the back quadrant is really no big deal at all for this IME.  Is anyone really going to remember or care which side everyone was on? Doubtful.   The biggest constraint with Blumlien is that the forward and backward facing main quadrants are so relatively narrow, it's sort of hard to fit all the important direct imaging sources in there.  One little known trick is to narrow the angle between microphones slightly, which widens the front and back recording angle quadrants a bit. Helps solidify the center too.

Not definite yet, but I'm hoping to make it up to Mag next month.  If so I'll be looking forward to seeing you at the porch stage Walter.

'Ambiophonics' is a playback arrangement using narrowly spaced speakers, electronic interchannel cross-cancellation techniques, and optional convolution reverberance.  It is ideally recorded using a front/back baffled and pinna-less dummy head.  But it often works for playing back standard stereo recordings too.  'Ambiophonics' doesn't really apply to coincident crossed figure-8 'Blumlien' stereo in anyway that I'm aware of. 

[Gutbucket]

Just gave a listen to the Youtube link. 
Life is grand when you get women singing backup in the right spots.

[cybergaloot]

Just gave a listen to the Youtube link. 
Life is grand when you get women singing backup in the right spots.

I'd go for the thinner one but she could probably outrun me. Well, no probably to it. I'm gimpier than ever. I need me a Rascal Scooter!

[cybergaloot]

Now I'm confused, which is a normal situation for me. I'll have to think it through when I'm not as tired as I am right now.

I'm really surprised the hired us for Magfest again. Never look a gift horse in the mouth I guess. I need to remember to pack my Patchbay II. I've got it stashed in the back of a rack under my board at the club. Easy to forget! But I'm getting a 16U rolling rack from JB Ritter (used to run sound at the camp ground stage) so I can put all my gear in one rack there. Right now my HD24 is behind me in separate rack which is a pain in the ass. Anyway, when I move things over the Patchbay will surface again.

[Gutbucket]

So is Corina going to be there?

[Tom McCreadie]

'Ambiophonics' is a playback arrangement using narrowly spaced speakers, electronic interchannel cross-cancellation techniques, and optional convolution reverberance.  It is ideally recorded using a front/back baffled and pinna-less dummy head.  But it often works for playing back standard stereo recordings too.  'Ambiophonics' doesn't really apply to coincident crossed figure-8 'Blumlien' stereo in anyway that I'm aware of.

No, I believe that's ambiosonics. For ambiophonics, look up some of the Sennheiser technical mic papers.

[DSatz]

Back in the 1970s I lent my Schoeps stereo mike to another engineer who recorded an album with crossed figure-8s set up in the middle of a quartet, and he liked it (or more precisely, thought that he was cool to have thought of the idea). And one very nice thing about figure-8s for direct sound recording in general is the way that any low-frequency diffuse noise in the room gets canceled out. Room rumble that can be a real problem with cardioids or omnis often goes away completely when you use figure-8s--not because of their low-frequency rolloff, but because of their equal-but-opposite sensitivity on the front vs. back of the diaphragm(s) (a simultaneous rise in pressure on both sides causes no net output). Also, there's no pickup from the ceiling or floor directions, which can be helpful when you have a low-ceilinged space.

About ten years ago I recorded a series of master classes with opera singers who were rehearsing in a circle. I used a pair of back-to-back cardioids, a setup which also rejuggles the left-right arrangement of the performers as Blumlein does, but it seemed to do so in a more straightforward way, perhaps. I mean, by the time you're using a coincident center mike setup, you're giving up on realistic left-to-right stereo imaging so it's just a matter of what gets you the tone and balance that you want.

--Someone earlier in the thread mentioned the IRT Cross arrangement. I translated all the product literature for Schoeps when they were introducing their surround products, and I'd just like to point out what they mean by "ambient" miking: It means that you're not trying to pick up direct sound because you already have some other miking setup for that. Instead you're literally trying to record ambience, background-level sound that augments the sense of spaciousness, that doesn't convey the main, direct information of the recording. Some of the surround arrays that Schoeps sells have microphones for picking up direct sound, but the IRT Cross isn't one of them.

--best regards

[cybergaloot]

So is Corina going to be there?

I don't know.

[Gutbucket]

'Ambiophonics' is a playback arrangement using narrowly spaced speakers, electronic interchannel cross-cancellation techniques, and optional convolution reverberance.  It is ideally recorded using a front/back baffled and pinna-less dummy head.  But it often works for playing back standard stereo recordings too.  'Ambiophonics' doesn't really apply to coincident crossed figure-8 'Blumlien' stereo in anyway that I'm aware of.

No, I believe that's ambiosonics. For ambiophonics, look up some of the Sennheiser technical mic papers.

Hi Tom.  Most definitely Ambiophonics. 

Wikipedia entry- http://en.wikipedia.org/wiki/Ambiophonics
Ralf Glasgal's website- http://www.ambiophonics.org/

The simple version using a mechanical baffle (sheet of cardboard, plywood, a mattress, or whatever) running between narrowly spaced computer speakers and the listener's nose is a cheap and easy experiment I recommend to anyone interested in stereo playback and phantom imaging.  The center of the playback image is provided from the actual speaker sources and phantom images extend out to either side depending on the stereo content of the recording.  Sort of the inverse of the way the standard stereo speaker triangle works.  The electronic cross-cancellation techniques aim to replace the awkward mechanical baffle with electronics.

I did a general search for ambiosonics and more or less came up empty.  I also checked the Senn site for both terms but couldn't find any related technical papers.   If you have any links, please let me know.  I'd like to read them.

[cybergaloot]

Too bad I need to be elsewhere this weekend because this would probably be a good place to test things: http://pickersparadisepark.com/

[Gutbucket]

--Someone earlier in the thread mentioned the IRT Cross arrangement. I translated all the product literature for Schoeps when they were introducing their surround products, and I'd just like to point out what they mean by "ambient" miking: It means that you're not trying to pick up direct sound because you already have some other miking setup for that. Instead you're literally trying to record ambience, background-level sound that augments the sense of spaciousness, that doesn't convey the main, direct information of the recording. Some of the surround arrays that Schoeps sells have microphones for picking up direct sound, but the IRT Cross isn't one of them.

That was me.  So does the same apply to double ORTF?

I realize that the typical use of IRT Cross arrangement and it's target market for Schoeps is for the provision of ambient background recording.   However, it can also be used as a primary mic array.  Consider that a pair of cardioids angled 90 degrees apart and spaced 25cm provides a Stereo Recording Angle of 90 degrees and is a typical near-spaced pair stereo arrangement.  The IRT Cross is simply four of those, one facing each direction, sharing microphones at the vertices. The second pair of microphones simply extends the forward facing stereo configuration to also face the sides and rear.  One can choose any two adjacent microphones in the array, ignore the others and the result is a typical near-spaced cardioid pair facing in that direction. 

Micheal Williams suggested an isotropic four cardioid arrangement with the same configuration as the IRT Cross in this AES paper back in 1991 with an emphasis on critically-linked imaging between each segment of the array, rather than simply the provision of a spacious ambient background 'bed' for use with other main microphones.  I assume that was the basis for the IRT Cross configuration.

Four Segment Array-
Hypercardioid microphones (Figure 6) - ll cm /90 °
Cardioid microphones (Figure 5) - 25 cm /90 °
Hypocardioid microphones (Figure 7) - 35 cm /90 °

Granted that doesn't cover issues with down-mixing down those resulting 4 channels to 2-channel stereo, but neither does Double ORTF, which Schoeps does market as a dedicated main microphone array as far as I'm aware.  The only difference between double ORTF and IRT-cross is the specifics of the near-spaced configurations in each quadrant and the overall array symmetries.

Please let me know if I'm missing something here, thanks!

[Tom McCreadie]

I did a general search for ambiosonics and more or less came up empty.  I also checked the Senn site for both terms but couldn't find any related technical papers.   If you have any links, please let me know.  I'd like to read them.

Sorry for the typo, Gutbucket, I was rushing out the door. That should have been ambisonic or ambisonics,  with only one "o".
But the ambiophonic I refer to is not a recording technique as such. It is really just a posh word to describe a region of the 360° space that will deliver stereo signals with out of phase parts (even with coincident, intensity-stereo recordings). Since one loudspeaker's cone will  then be pumping forward while the partner speaker's cone is pumping baclwards, it's unsurprising that the playback imaging will deteriorate.

As you pointed out, the ambiophonic effect adds a spaciousness to the recording, and a precise imaging of audience etc. is mostly irrelevant, anyway, in a typical Blumlein scenario where the performers are placed in the front quadrant . The OP of this thread, however, did specifically ask about handling musicians  "sitting in a circle". So It seemed prudent to mention that those pickers unlucky to be seated in the two Bermuda Triangle sectors, L  and  R of the centred Blumlein pair, might whinge that they got a raw deal   :-)

That very useful Sennheiser article was originally a paper publication: 

"XY and MS Stereo Recording Techniques" (by Manfred Hibbing).

Mr. John Willett, who has an association with Neumann and Sennheiser, arranged for a pdf of the paper to be made, and kindly offered to supply it to any interested folks on the Gearslutz/ Remote Possibilities...  web forum.  He emailed me the pdf. Perhaps I can upload a copy: How?: PM?, or Dropbox? (<-not permanent link)  In any case, I prefer to first clear that from Mr. Willett. (Maybe he can  now supply an existing link.)

[Gutbucket]

Thanks Tom, that clears things up.

Ambisonics is basically Michael Gerzon's a direct extension of Alan Blumlein's coincident stereo Mid/Side technique to three dimensions.  It's a beautifully elegant and mathematically rigorous approach which provides amazing control over manipulating coincident stereo. 

I have an ambisonic microphone and have learned a lot from recording with it and playing around with various ways of decoding the resulting recordings.  I didn't mention it since it's not something immediately available to the OP and the discussion gets complex, but I can see it being useful for this particular situation for a few reasons: 

First the single microphone is far less imposing than some of these other suggestions, it would hardly impose much on the social situation placed in the center of the circle.  Second, after the recording has been made, the resulting four channel output can be manipulated after the fact to point virtual microphones of any standard first-order pattern in any direction.  That doesn't mean that a pair of back-to-back cardioids might not be the best sounding choice and that a recording made with an ambisonic microphone would necessarily be better, but it does mean that you gain control over re-pointing those cardioids however you'd like after the fact.  You also can vary the pickup pattern of those two virtual microphones from cardioid towards figure-8 or the other way towards omni.  So you can play around with microphone arrangements after the fact to find what works best, then as the makeup of players changes around the circle from song to song and the focus changes from one area of the circle to another, you could re-point the microphones as appropriate.  That might all be more involved than necessary or appropriate, but it's entirely possible.

Ambisonics does have important limits though: First, it's limited to coincident techniques, so unless used in combination with other microphones, any time-based stereo techniques are out.  Second, first-order ambisonics, which is the limit of current ambisonic microphones, works well for 2-channel stereo output and up to at most 4 channel surround.  It cannot provide the channel separation required for robust surround sound for music recording with more than 4 playback channels.  You need space between microphones in a array to achieve that.  It does Blumlein very nicely with the ability to tilt and point the array though, and could also do four cardioids in an 'X', just without any spacing between them.

I've only played with ambisonic stereo decoding and some limited 4 and 5 channel surround output.  I'd love to hear a true ambisonic reproduction system, which places speakers at the vertices of a geometric solid and doesn't mess around with pointing virtual microphones this way and that for stereo decodes or typical multi-channel playback, but instead aims to reproduce the sound-field as sampled by the single-point microphone during the recording at the point in space located at the center of the playback array.  At a minimum, that requires 8 speakers located at the corners of a cube in 3-dimensions.  A circle of pickers with people milling about behind them laughing and having a good time while the trees rustle overhead in the breeze may well be the perfect demo for that!

[cybergaloot]

The OP is too poor to own an ambisonic microphone when what he really needs is a decent set of of drum mics.

[Len Moskowitz (Core Sound)]

Ambisonics does have important limits though: First, it's limited to coincident techniques, so unless used in combination with other microphones, any time-based stereo techniques are out. ...

In some ways, considering this a limitation is like saying that a cardioid mic is limited because it can't do stereo recordings. It really can, but it takes two of 'em!

As we've discussed in other threads, you can use two or more ambisonic mics to do time-based stereo techniques.

And by the way, we keep a good stock of Jecklin and Schneider Disks.

[capnhook]

Too bad I need to be elsewhere this weekend because this would probably be a good place to test things: http://pickersparadisepark.com/

"bout time Doug Oade's sleepy old hometown gits itself some culture.....looks fun.

[Gutbucket]

Does look like a nice low-key good time.

My apologies for getting this so far off topic..

Ambisonics does have important limits though: First, it's limited to coincident techniques, so unless used in combination with other microphones, any time-based stereo techniques are out. ...

In some ways, considering this a limitation is like saying that a cardioid mic is limited because it can't do stereo recordings. It really can, but it takes two of 'em!

As we've discussed in other threads, you can use two or more ambisonic mics to do time-based stereo techniques.

Sure, but the resulting multi-microphone recordings will no longer be ambisonic..  even though the feed from each individual ambisonic microphone is.  Ambisonics always deals with the soundfield and it's recreation at only a single point in space.

I feel it important to emphasize that ambsionics is not the end all be all of recording, even though it is indisputably an amazing and useful approach, and far more accessible than it once was thanks to tools like the relatively low cost ambisonic microphone Len has made available (The ambisonic microphone I use is his Core TetraMic).

However, if anyone reading is interested in all this somewhat arcane ambisonics stuff, there are some very costly and very heavy processing intensive ambisonic recording methods which do extend beyond the limitations of standard first-order microphone patterns.  Most of them deal with measurement and industry and aren't very suitable for music recording but I know of at least one which is.  It uses eight omnidirectional microphones arranged in a specific 2-dimentional pattern to derive virtual polar patterns of up to the 5th order, limited to the horizontal plane in this particular implementation.  Even though it uses multiple omnis distributed in space rather than four directional microphones arranged as closely as possible to the same point in space, its output is still limited to coincident patterns by the nature of ambisonic theory itself. Here's a link to the PDF from Trinnov Audio.

[cybergaloot]

Too bad I need to be elsewhere this weekend because this would probably be a good place to test things: http://pickersparadisepark.com/

"bout time Doug Oade's sleepy old hometown gits itself some culture.....looks fun.

I haven't seen or heard from him in quite some time.

[Len Moskowitz (Core Sound)]

Sure, but the resulting multi-microphone recordings will no longer be ambisonic..  even though the feed from each individual ambisonic microphone is.  Ambisonics always deals with the soundfield and it's recreation at only a single point in space.

Thanks for the very kind words about TetraMic.

If "ambisonic recording" means that a recording is made using only one ambisonic microphone, I think that's too limiting a way to think about it.

Ultimately, an ambisonic microphone is just another source of the audio tracks used to playback a recording. Its decoded output can be mixed with other sources of audio, which might include fixed pattern mics or other ambisonic microphones. In the final mix there should be no way to know whether the source of the audio is an ambisonic microphone or a fixed pattern mic.

Let's imagine we were recording an orchestra. We could position an ambisonic microphone behind and above the conductor and decode its output to - let's say, Blumlein. In post-production we could mix that with the output of another microphone - say a fixed-pattern hypercard spot mic positioned close to a soloist.

Or we could use two ambisonic microphones. One would be set up as before - behind and above the conductor, and decoded to Blumlein. The second ambisonic microphone could be positioned close to a soloist and decoded to hypercard.

The two resultant recordings would be near identical (though I say kind of proudly that it's very possible the second might have a better hypercard). Whether either of them is an "ambisonic recording" is really irrelevant, no?

The same goes for ORTF or other spaced arrays created by using more than one ambisonic mic.

'Nuff said.

[Gutbucket]

Aesthetically, I fully agree that it doesn't matter what labels are placed on all this other than subjective things like "good sounding" and "believable or not" with regards to the end result.  Music recording and playback is all about the creation of an illusion anyway.  However, from a technical perspective (this is something of a technical recording forum after all) what you describe above is two ambisonic recordings, the first decoded to two channel stereo, the second decoded to single channel mono, which are then mixed together in two-channel stereo non-ambisonically.  The end result is a two-channel stereo recording.

The distinction is important in differentiating what techniques are used and how to go about manipulating things, rather than describing the quality of the result perceived by a listener.  It's an important one in a technical discussion of how the equipment is used and the recordings are made.

Nothing stops us from using all these tools creatively.  I've made numerous recordings using a stereo decode from the TetraMic plus a spaced pair of omnis.  The resulting recoding is 2-channel stereo and not ambisonic.  Part of it was made ambisonically, part of it made as A-B spaced omnis stereo.  The ambisonic portion left the ambisonic domain when I chose one particular stereo decode of it.

I could describe alternate mixing options for your two ambisonic microphone scenario, done within the ambisonic domain without first decoding from B-format, which would be an entirely different procedure and have very different sonic implications.  Unless played back over an ambisonic loudspeaker array, the resulting output would most likely be decoded to stereo, multi-channel, binaural, or whatever for listening and would at that point no longer be ambisonic.  These are important distinctions to make on a recording forum describing how the tools are used, which aren't important at all from the perspective of the listener.