Topic: Cardioids which are most natural sounding off-axis? On-axis sound secondary.

[Gutbucket]

I'm thinking about various cardioids for the specific application of recording audience reaction and room ambience, both for 2-channel stereo mixes and for descrete surround channels.  The microphones in this case are being placed so they are facing 'backwards', directly away from the primary source of the music, which is intentionaly placed in the least sensitive portion of the microphone's pickup pattern.

While the music is playing, the primary sound souces from the front are the loudest sounds arriving from any direction, so to help keep the sound arriving from that maximally rejected direction sounding as natural as possible, an important requirement of these microphones is a particularly well behaved off-axis response.  The on-axis response in this case is actually secondary.

In addition, the total contribution of these ambient/audience channels is always secondary to the primary microphones, so although they do need to sound natural on-axis as well (or rather across the entire rear-facing hemisphere) for their contribution to be appropriate, their good off-axis behavior is more significant in that it not interfere with what the primary microphone are providing.

This doesn't change the standard measure of what makes for a well behaved directional microphone polar response, it just flips the primary measure of importance from the on-axis response to the off-axis response.

So I'm wondering if there may be cardioids with excellent off-axis response, which may not be a first choice on-axis wise.  Odd request I realize, partly just thinking about the implications here.

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I know the Neumann KM143 or AK43 caps allow for a wide-angle card pattern recording.  I use them in odd shaped rooms for that specific purpose, although I am not sure this fits what you may be looking for in regards to the pattern and facing backwards?

[bombdiggity]

I'd think you're looking for a very narrow angle card pattern so that all you're really getting is what is coming straight toward the mics from the crowd.  What you picked up on the sides of these would be sound from the stage, which you don't want in this application (and which I'd think might be inverted or at least out of phase relative to the primary signal on the music-facing mics?).  I don't know what mics specifically but seemingly a narrow pattern designed for near field sound (rather than for sound at a distance, since that might start to pull in the echo from the back bouncing toward the rear facing mics, which would be even further out of phase). 

[Gutbucket]

wide-angle card pattern

Subcards seem generally well behaved off-axis and possibly a good consideration for this, the only issue is their more limited rejection behind them (the front in this case).  But if their reduced sensitivity in that direction is signifcant enough a pair of subcardioids may be the answer.  That reduced sensitivity is generally smoother across the back in level as well as frequency response, which would also be an advantage.

A small lightweight, not too expensive, low-voltage subcard would fit this appication nicely.  Now that the AT853 subcard is a rarity (I never used them and not sure how well behaved it is or how attenuated it is to sound from the back) what other similar subcards might be considered?

[Gutbucket]

I'd think you're looking for a very narrow angle card pattern so that all you're really getting is what is coming straight toward the mics from the crowd.  What you picked up on the sides of these would be sound from the stage, which you don't want in this application (and which I'd think might be inverted or at least out of phase relative to the primary signal on the music-facing mics?).  I don't know what mics specifically but seemingly a narrow pattern designed for near field sound (rather than for sound at a distance, since that might start to pull in the echo from the back bouncing toward the rear facing mics, which would be even further out of phase).

Actually the opposite- preferably a wide 180 degree acceptance pattern to the rear with a diffuse-field response.  The intention is to capture the ambient room sound as well as the audience response.  Ideal would be something like boundary mounted omnis facing rearward, with clear ambient pickup of all sound arriving from the rear hemisphee, and maximal rejection (but more importantly, well behaved rejection) from the front hemisphere.  I've boundary mounted omnis to the stage lip facing out and they do this job very well.  However, this application is for a typical stand-mounted config where that's not applicable.. and that's why the question of well behaved off-axis response with significant enough rejection comes into play.

These will be more or less A-B spaced facing rear-wards, probably with little to no angle between them, though perhaps up to 90 degrees, but no more than that.

There are no reversed polarity issues to be concerned with if the polar pattern has no reverse polarity lobe.  The output of a cardioid, subcardioid or omni will have the same polarity regardless of the angle of incidence.

[bombdiggity]

I'd think you're looking for a very narrow angle card pattern so that all you're really getting is what is coming straight toward the mics from the crowd.  What you picked up on the sides of these would be sound from the stage, which you don't want in this application (and which I'd think might be inverted or at least out of phase relative to the primary signal on the music-facing mics?).  I don't know what mics specifically but seemingly a narrow pattern designed for near field sound (rather than for sound at a distance, since that might start to pull in the echo from the back bouncing toward the rear facing mics, which would be even further out of phase).

Actually the opposite- preferably a wide 180 degree acceptance pattern to the rear with a diffuse-field response.  The intention is to capture the ambient room sound as well as the audience response.  Ideal would be something like boundary mounted omnis facing rearward, with clear ambient pickup of all sound arriving from the rear hemisphee, and maximal rejection (but more importantly, well behaved rejection) from the front hemisphere.  I've boundary mounted omnis to the stage lip facing out and they do this job very well.  However, this application is for a typical stand-mounted config where that's not applicable.. and that's why the question of well behaved off-axis response with significant enough rejection comes into play.

There are no reversed polarity issues to be concerned with if the polar pattern has no reverse polarity lobe.  The output of a cardioid, subcardioid or omni will have the same polarity regardless of the angle of incidence.

Ah.  Sort of a half omni?  The boundary thing does come to mind... 

My brain tends to melt with the things you try McGyver... 

I was sort of thinking of the issues you'd get if you mic a drum from bottom and top as an analogy to micing a PA in effect from front and behind. 

I'm never a fan of diffuse/omni/crowd noise/venue reverb/etc. so have never tried any of these sorts of things.  From your explanations of what you're after I think I get the idea but the technique remains foreign.  I read to push my thoughts on all this in different directions though. 

[Gutbucket]

I was sort of thinking of the issues you'd get if you mic a drum from bottom and top as an analogy to micing a PA in effect from front and behind.

Two differences-
Extending your analogy, I don't know of any PA's that are dipolar in radiation like a drum.  They are omnidirectional to cardioid-like in their radiation, and don't have inverted polarity radiation to the rear. Secondly, even if the PA did radiate as a dipole, all my microphones are placed on the same side of the 'drum'. 

I'm never a fan of diffuse/omni/crowd noise/venue reverb/etc. so have never tried any of these sorts of things.

 
I think you are more than you realize, unless you always prefer a straight, bone-dry SBD.  It's really more a question of how much is the 'right' amount, which in part hinges on it's quality.  It's 'too much' if it is objectionable, outright bad, or even if it's good but there is simply too much of it.   No question that the optimal amount is ultimately a subjective determination, where we may have different personal preferences.  However, its not really a black and white issue but is essentially a shades of grey thing.

[edit- I don't question that you get more than enough "diffuse/omni/crowd noise/venue reverb/etc." in whatever two-channel arrangement you are using.  Part of what I'm doing with this is gaining more control over that relationship.]

[bombdiggity]

I was sort of thinking of the issues you'd get if you mic a drum from bottom and top as an analogy to micing a PA in effect from front and behind.

Two differences-
Extending your analogy, I don't know of any PA's that are dipolar in radiation like a drum.  They are omnidirectional to cardioid-like in their radiation, and don't have inverted polarity radiation to the rear. Secondly, even if the PA did radiate as a dipole, all my microphones are placed on the same side of the 'drum'. 

I'm never a fan of diffuse/omni/crowd noise/venue reverb/etc. so have never tried any of these sorts of things.

 
I think you are more than you realize, unless you always prefer a straight, bone-dry SBD.  It's really more a question of how much is the 'right' amount, which in part hinges on it's quality.  It's 'too much' if it is objectionable, outright bad, or even if it's good but there is simply too much of it.   No question that the optimal amount is ultimately a subjective determination, where we may have different personal preferences.  However, its not really a black and white issue but is essentially a shades of grey thing.

[edit- I don't question that you get more than enough "diffuse/omni/crowd noise/venue reverb/etc." in whatever two-channel arrangement you are using.  Part of what I'm doing with this is gaining more control over that relationship.]

 

Well yeah.  I meant that in a relative sense since there's always some degree of all that in an ambient recording.  I'm probably far off that scale compared to many though.  I like recordings/rooms considerably more dry than my sense of what most others seem to like.  I do like just a touch of air in them but am probably hyper sensitive to room dynamics (I was talking with one of my musician friends who was also recording rooms we were in about the differences between them and what I thought was better or worse - one room I like more as a listener but less as a recordist and vice versa among two in particular).   We seemed to agree on our assessment of most of the spaces (which in her case is based in part on how it feels playing in them) but she was puzzled as to why one she liked a lot didn't seem to record as well as you'd think it should.  I was surprised until I thought about the room more after a few visits.

A sense you're in the room (more from immediacy and presence than from reverb) and that there is some dynamic to it is all I want.  I don't want to hear the crowd other than in between songs (the clapping for every solo thing that jazz audiences seemed to be trained for drives me a bit batty and can wreak havoc with levels unamplified in a small room).  I don't really want to hear the room reverb, just sense it.  At the point I hear any of that as echo I'm past where I want to be (though can't count the number of comments I see on sites about how great sounding really boomy recordings are). 

Vocalists almost always like more effects/reverb on their voices than I do.  The vocal thing I liked most was a house concert we did with some singer/songwriters that was totally unamplified.  Just two (and occasionally four) vocals with an acoustic guitar/occasional uke.  That's the true test of a singer though.  It takes a lot of confidence and experience to do that and sound beautiful.  A few of the contemporary folk crowd (which I rarely follow in broader terms) really seem to know how to do that though. 

For that I ran the pair of 4V's spread on the corners pointed 45 degrees in toward the point between the two of them, which I had not tried before, but I wasn't keen on throwing mics up directly in front of them since it was a really full crowd right up to the "stage" area and for recording only that seemed sort of rude, even if it was my house.  It really captured the way I'd want to hear it though. 

Your approach of controlling the relationship by more points and angles is interesting (and challenging).  I think you're after a slightly different perspective than I am.  My approach is more to control it by seeing the whites of their eyes.  I like to try to get an ambient sound stage with locational references while being really close (and more in a conventional stereo plane where I think you've mentioned a custom surround sort of listening environment that may be uniquely yours).  I've never wanted to add more audience than what comes through from my point (typically in front of all of them).  Often I'd rather like to remove a few elements of that ;-/ .   

[voltronic]

I've posted about these mics before, so apologies if they are old news to you.  They are inexpensive and have a polar response that might suit your needs.  Those who own them supposedly get great results in a NOS array especially.  I'm buying a pair once my tinybox arrives.

http://www.lineaudio.se/CM3.html

Many samples and discussion found on the long GS thread here:
http://www.gearslutz.com/board/remote-possibilities-acoustic-music-location-recording/644759-cm3-really-good.html
...especially impressive are the vocal samples in this post:
http://www.gearslutz.com/board/8080039-post396.html

But what really sold me on them was this album, recorded with just one pair straight into a SD 702.  Not at all how you would be using them, but gives you an idea on their quality:
http://elswhr.co/projects/lumiere

[John Willett]

I'm thinking about various cardioids for the specific application of recording audience reaction and room ambience, both for 2-channel stereo mixes and for descrete surround channels.  The microphones in this case are being placed so they are facing 'backwards', directly away from the primary source of the music, which is intentionaly placed in the least sensitive portion of the microphone's pickup pattern.

While the music is playing, the primary sound souces from the front are the loudest sounds arriving from any direction, so to help keep the sound arriving from that maximally rejected direction sounding as natural as possible, an important requirement of these microphones is a particularly well behaved off-axis response.  The on-axis response in this case is actually secondary.

In addition, the total contribution of these ambient/audience channels is always secondary to the primary microphones, so although they do need to sound natural on-axis as well (or rather across the entire rear-facing hemisphere) for their contribution to be appropriate, their good off-axis behavior is more significant in that it not interfere with what the primary microphone are providing.

This doesn't change the standard measure of what makes for a well behaved directional microphone polar response, it just flips the primary measure of importance from the on-axis response to the off-axis response.

So I'm wondering if there may be cardioids with excellent off-axis response, which may not be a first choice on-axis wise.  Odd request I realize, partly just thinking about the implications here.

The Gefell M300 are pretty consistent off-axis (except for the very highest frequencies, where body size comes into play).

The Sennheiser MKH 40 is also good in this respect (NB: you have to download the owners manual to see the diagrams).

[DSatz]

Sorry to be late to this party (thread)--this issue is the one that, in my opinion, points to the real value of the very best small microphones.

The ideal, if it suits your recording environment, must be a high-quality Blumlein pair. A pure pressure-gradient transducer that is small enough can be made to have essentially no audible off-axis peaks. Not many recording environments work well with this recording technique, so I would never walk into a new venue with only a Blumlein setup and expect to make it work well, but when it does work well the realism can be amazing.

If the directional pattern absolutely must be cardioid (which is in some ways "the worst of both worlds" between being a pressure and a pressure gradient transducer), then I suggest cardioids that are "radially addressed" (so-called "side-firing"). Look closely at the 8 kHz polar diagram because that will be closest to where the problem area usually occurs. Examples would include the Schoeps MK 4 V (if its high-frequency response profile suits you) and (especially) the cardioid setting of the now-discontinued MK 6. Unfortunately Neumann no longer makes small-diaphragm microphones of this kind, but Sennheiser has a multi-pattern model (which I've never tried) that is supposed to be quite good.

But I would suggest even more strongly that you consider patterns that are "cardioid-adjacent" as others have mentioned in this thread. I generally find that wide cardioids (Schoeps MK 21, Neumann KM 143) require careful placement, and (as with Blumlein) there are relatively few environments in which they sound their best--though when that occurs, it's definitely worth it.

As a more general solution, currently when I need directional microphones that bring out beauty of tone and reduce the harshness of some acoustical environments, I use the Schoeps "open cardioid" (MK 22). It works very well in stereo pairs. As an alternative that picks up a higher proportion of direct sound energy, I use supercardioids (Schoeps MK 41, with Neumann KM 150 as an alternative if its particular frequency response fits the requirements--it is light in the bass and has the little treble peak that has unfortunately become part of Neumann's "house sound" for their small-diaphragm directional microphones since the 1980s).

--best regards

[bombdiggity]

I've posted about these mics before, so apologies if they are old news to you.  They are inexpensive and have a polar response that might suit your needs.  Those who own them supposedly get great results in a NOS array especially.  I'm buying a pair once my tinybox arrives.

http://www.lineaudio.se/CM3.html

Many samples and discussion found on the long GS thread here:
http://www.gearslutz.com/board/remote-possibilities-acoustic-music-location-recording/644759-cm3-really-good.html
...especially impressive are the vocal samples in this post:
http://www.gearslutz.com/board/8080039-post396.html

But what really sold me on them was this album, recorded with just one pair straight into a SD 702.  Not at all how you would be using them, but gives you an idea on their quality:
http://elswhr.co/projects/lumiere

Thanks for the tip.  News to me.  The album sounds great and is the sort of thing I sometimes record and need small mics for, though I don't have my choice of placement for those.  At the price point I may want to try these.  Seems hard to go too wrong. 

[raymonda]

Schoeps have about as perfect cardioid pattern as you'll find.

[notlance]

Gutbucket, don't you own an ambisonics microphone?  Seems to me that would work well in this situation, if you have the channels available.

For fewer channels, (well, one less) you could try a Double MS setup that would give you a lot of control over pattern and direction.  But you already know all about that.

As for a specific microphone, the Sennheiser MKH-800 and MKH-800 Twin have good off-axis response.  Get one of each and do that DMS thing.  Or the Milab DC-196 and DC-96C are very nice off-axis too.

[Gutbucket]

Thanks to everyone for input on appropriate practical solutions for this application as well as discussion the conceptual aspects involved.

I certainly like what I’ve heard of recordings made with Schoeps MK 4V & MK 21, and I have two pair of Microtech Gefell microphones I’m currently using in other positions in this setup, although slightly different models than the one John mentioned. All these including the Senheissers are excellent suggestions I’d love to try, but unfortunately cost prohibitive given the secondary roll these will be playing in this array.

Thanks for the reminder of the Line Audio CM3, which is in a more appropriate price range and which I’ve been interested in but had forgotten about.   

Yes, I have a Tetramic, but it’s not what I’m looking for in this application for a few reasons: it is restricted to coincident patterns rather than the spaced A-B configuration this setup is using, it requires 4 channels, and requires separate decoding.  I’m using this as part of a spaced configuration surround recording setup which is in some ways the opposite approach to a single-point ambisonic approach, and this setup is already complex enough without those extra channels and decoding steps.


Later I’ll post a few more thoughts on the conceptual aspects. For now, here’s specifics on what I’m doing- 

These are to serve as part of a multichannel rig (currently using 6 microphones) which I use for recording performances in good sounding outdoor environments.  These microphones will be used for rear-facing ambient/surround channels in an Optimum Cardioid Triangle + surround array, for both multichannel surround and stereo.  Here’s a link to a page describing the standard 3-channel OCT setup at the Schoeps website and DPA websites and a brief description of OCT + surround (the surround part is the job of these microphones) on the Schoeps page. 

The Gefells I’m using in this array are a pair of M94/MV692 cardioids and a pair of M210 supercardioids, and I’ve been very pleased with the performance of both pairs.  One M94 is used as the forward facing, center cardioid.  The M210s are used as the sideways facing supercardioids. The other single M94 is currently being used as a single rear-facing audience/ambience cardioid in back, basically mirroring the front center.  Rather than that single rear-facing microphone I’m looking to emulate the OCT + Surround setup shown at the Schoeps link with a spaced pair, which was motivation for this thread.

Also part of this array currently is a pair of wider spaced omnis, about 6’ apart in the same plane as the OCT supercardioids.  They are intended partly for extending the low end response of the directional Gefells, as well as for ambient pickup and alternate uses as surround channels.  All six microphones currently in use are being powered by and recorded into a Tascam DR-680.

It is interesting comparing the contribution of the omnis against the single rear-facing center cardioid.  When routed directly to the surround playback channels rather than as part of a 2-channel mix, the omnis do a really excellent job, except for picking up a bit too much direct sound from the front.  To avoid pulling the front image around into the surround channels, the playback level of the omnis needs to be lower than is would otherwise be optimal.  The single rear facing M94 provides sufficient isolation from the front allowing is use at higher levels but is lacking in low end response, and as a single channel it provides a more limited sense of width and envelopment and none of the nice reverberant decorellation.

The omnis are especially natural sounding, but require riding levels to bring them up to their optimal level between songs and in the quieter musical sections, then down in level when the music gets louder to keep the image properly anchored in front.  Similarly in a stereo mix, the greater isolation allows use of more ambience while retaining a cleaner mix.

I’ve working on two versions of this setup.  The “no-holds-barred” version is this one, using the full-body Gefells. 

I may replace the omnis with backwards facing subcardioids (remains 6 channels). Alternately I may replace the single rear facing center cardioid with this rear facing spaced pair pretty much like the standard OCT + surround setup but with the extra omnis (7 channels) or even increase the channel count to 8 and try it include them all.  Then after running it a few times I can whittle the channel count back down to what I find to be most essential.

The other version of the setup uses the same spacing and configuration, but substitutes miniature, less costly, low-voltage microphones for the Gefells. I haven’t yet fully configured that one as an OCT + configuration using side-facing supercardioids, but have used it only as a 4 channel version with the spaced omnis + front/rear facing miniature supercardioids.

[Gutbucket]

I'm sure that all sound ridiculously over-complex, but it really works very nicely.  Except for attaching the Gefells to the XLRs, it's pre-rigged and not at all complicated to setup.  I tend to test these more complex variations a few times, and then make a better informed decision on what is and what isn't important and refine things from there.

The omnis in both cases are miniature DPA 4061.  I can easily see an appropriate pair of miniature low-voltage cardioids or subcardioids working perfectly fine as rear facing microphones in both the heavier/high-quality and lighter/more-economical rigs.  So I suppose the next practical question is which miniature low voltage directional microphones sound natural enough well off-axis, recognizing that they are unlikely to be as well behaved as the high quality microphones metioned earlier in the thread are the effective ideal?

If a subcard pair has enough low end response, they could possibly take the place of 4061, reducing the channel count to 5, or keeping it at 6 if the center rear cardioid is retained.

[Gutbucket]

So here's a few thoughts which were bouncing around in my head when I started the thread, and which I now realize is what I really wanted to discuss most (even though I asked for specific microphone suggestions, and thanks for those)- 

What is the ideal off-axis response in comparison to the on-axis response?  Might it differ by application and perhaps by polar pattern as well?  Is an omni with an off-axis response which is identical to the on-axis response a measurement ideal or an musically appropriate ideal?  Is an off-axis response that is identical to the on-axis response in all aspects except for a difference in signal level that is constant with frequency musically ideal for a directional microphone?  These are clearly quantifiable and challenging engineering ideals, approached by some of the top quality directional microphones mentioned in this thread.  Stereo recording setups are often devised based on simplified modeling of microphones with this type of idealized behavior, as are the visualization programs which are commonly linked to around here. 

I’m intentionally asking these questions rhetorically.  I know (or believe I know) some of the reasoning behind all this, but I’m intentionally questioning both my own experience as well as common practice in trying to better assess what the appropriate ideal response might be for various applications. 

Here’s two specific examples, the first common, the second more of what I’m trying to get at with this-

All but the very smallest omnis with capsule and housing diameters become increasingly directional at high audible-range frequencies can be used to advantage rather than simply being considered an inevitable engineering tradeoff of capsule diameter.  Musical feature or bug?

It strikes me that some 180-degree off axis cardioid responses appear very similar in shape to human perceptual equal loudness curves.  If accurate enough and smooth enough, might that kind of response be advantageous if leveraged in such a way that sounds arriving from off-axis become loudness curve filtered as their level drops compared to the on-axis response?   I'm imagining a 90 degree off-axis cardioid response which emulates the -6dB down human hearing loudness curve from whatever the designer chooses as a nominal on-axis response level, with increased curve filtering for sounds arriving from farther to the rear producing signal levels lower than -6dB and less so for sounds arriving from angles more on-axis with levels higher than -6dB, morphing smoothly to whatever the target on-axis response is: free-field flat, a far-field diffuse curve, or whatever.

Is the answer 'perhaps so for some applications but it's too complicated to engineer that kind of behavior correctly'?

[fguidry]

Neumann M50 for Decca Tree arrays immediately spring to mind.

http://repforums.prosoundweb.com/index.php?topic=36013.0

http://repforums.prosoundweb.com/index.php?topic=2413.0

Fran

[Len Moskowitz (Core Sound)]

So I'm wondering if there may be cardioids with excellent off-axis response, which may not be a first choice on-axis wise.  Odd request I realize, partly just thinking about the implications here.

This was mentioned, and I see that you considered it: TetraMic or any other well-calibrated ambisonic microphone can be decoded to give you an excellent solution. What you're calling "off-axis response" can be as good as you want it to be. What makes it probably the world's finest Blumlein can make it one of the finest cardioids with excellent off-axis response.

And for what it's worth, even though their native patterns are never used, the capsules in TetraMic are sub-cardioids.

If you want non-coincident patterns, you can use more than one.

I see that you also want to avoid recording four channels and having to decode. Please keep in touch with us - we're working on some really good stuff.

[Gutbucket]

Len, I have thought a lot about this while playing around with virtual microphone patterns from the Tetramic.  It has the potential to be an excellent tool for exploring these questions given the appropriate decoding tools. This is one area in particular where the virtual pattern synthesis capabilities of an ambisonic microphone system like the Tetramic makes possible things we cannot otherwise achieve or test easily.

Can you point me to any B-format tools which can do the following?

1) Specify a changing polar response which varies between any two first order patterns, smoothly by frequency.
2) Specify a changing frequency response which varies between two user specified curves, an on-axis response and a 180-degree off-axis response, varying smoothly by angle of incidence.

Those tools would be a huge help in answering the questions I’m posing here by providing the ability to hear these things in real-world situations by isolating the differences to only these issues without such a wide range of other complications.  It won't make the Tetramic a practical answer for the particular microphone array application I described earlier, but it would definitely provide a way of getting real-world answers to these conceptual questions and is likely to have other real-world recording applications.

Glad to hear some new things are in the works at Core Sound in regards to the Tetramic. As a longtime Tetramic user, here are two basic issues I urge you to address to make the Tetramic more user friendly:

1) VVMic for TetraMic (and VVTetraVST) needs the ability to do basic A-format channel-matching gain adjustment in the standalone application.  This is a basic, critical A-level function. The user should be able to input test tone files made during a particular session for mic-preamp level calibration, determine the gain offset between each of the 4 files, and adjust for that in the application immediately prior to the A-format conversion.  To do so it would simply require a signal level offset detector and individual A-format channel gain controls.  The user should not be required to first import A-format test tone files to an editor, determine the gain offsets between channels, then import the audio A-format files, apply the calculated gain adjustments to them and export the files with those changes before being able to do an A-format conversion on them. 

2) A small, single-box power supply eliminating the need for the four separate power supply boxes and the mess of cabling.  It should have the option of either battery or P48 powering, with a 6pin mini-xlr input and a single mulit-pin output with various breakout cable options to suit various recorder inputs (XLR, ¼” TRS, unbalanced 1/8” TS plugs, etc).

[edit- Okay, after typing the bit above I just checked the Coresound site and it looks like you are providing some additional powering options with the new PPA3 and PPAc options.  The PPA3 effectively addresses simpler P48 powering.  What is still needed is a simple single-box battery supply, allowing any 4channel recorder to be used regardless of phantom powering.  That would make Tetramic>battery-box>Tascam Dr2d (4ch via two 1/8” inputs) the smallest/simplest ambisonic recording system available.]

[Gutbucket]

Neumann M50 for Decca Tree arrays immediately spring to mind.

http://repforums.prosoundweb.com/index.php?topic=36013.0

http://repforums.prosoundweb.com/index.php?topic=2413.0

Fran

Yes. That's a good example of a microphone which has a directional response that is not uniform across its frequency range, yet is highly desirable for some applications partly because of that trait.

To continue the latest ambisonic twist on all this, a simplified/idealized version of that M50 polar response behavoir (pressure omni mounted in a spherical housing) could be relatively easily modeled by ambisonic B-format manipulation techniques.  Len, do you know of any B-format software tools which offer that?  It could be modeled in the B-format tool I asked about above, one which allows the user to "Specify a changing polar response which varies between any two first order patterns, smoothly by frequency".  In this case, omni up to the corner frequency where the size of the spherical plastic housing around the capsule becomes acoustically significant, then smoothly morphing to a more directional pattern on-axis at frequencies above that. 

[Gutbucket]

Perhaps.  Are there no balun components in the receiver necessary to convert the CAT5/6 run to mini-plug appropriate?  But yeah, that's a step closer to what I'd like for more minimal setup for powering the TetraMic.   Still requires a seperate external battery though, so perhaps not significantly different enough in size, weight and complexity from 4 x PPA2 boxes gaff-taped together into a block, which is how I currently power it.

What TetraMic needs is a simple battery box with two 6-pin mini XLRs.  One for input from the existing 6-pin mini-XLR terminated mic cable, the other to a 2 x miniplug output breakout (in my case, or whatever output terminations are appropriate)

In Niaint product line terms, it needs a 4channel PIPsqueek.  The 3 position global gain switch and independant channel gain balancing feature would be perfect for running a TetraMic into a DR2d.  The entire ambisonic recording system would fit in one hand.

[Gutbucket]

In a similar vein to my speculation about the possible usefulness of an off-axis response which is 'loudness curve' shaped, here's another observation from looking at the responses of existing microphones.  It may or may not be useful, but what about a flatter 'free-field' on-axis response with an elevated high-frequency 'diffuse-field' off-axis response?  Sort of the opposite of the typical real-world omni high-frequency directional response exaggerated in the M50.  I can't see that being useful for distance mic'ing, but it might be for closer mic'ing of a source where a free-field response is appropriate, while retaining diffuse-field ambient pickup qualities.

Although it's not free-field equalized on-axis, the on-axis/off-axis response difference of my Gefell M94 cardioid capsules looks a bit more like that, with much less low frequency 'loudness curve' and a touch more diffuse-field-EQ-like 9kHz emphasis in the 180-degree off-axis response than their M300.  Granted that in comparison, the on-axis low frequency response of the M94 drops compared to the M300, so its 180-degree off-axis is lower by that same amount, but even so, the difference between the curves is less than the more loudness-like 180degree off-axis curve of the M300 cardioid.

MG M300 cardioid microphone (180 degree off-axis response more loudness-curve like)-


MG M94 cardioid capsule (180 degree off-axis more diffuse-curve like, even if one imagines both these curves modified once the on-axis is normalized to match the M300 curve)-

[Len Moskowitz (Core Sound)]

Can you point me to any B-format tools which can do the following?

1) Specify a changing polar response which varies between any two first order patterns, smoothly by frequency.
2) Specify a changing frequency response which varies between two user specified curves, an on-axis response and a 180-degree off-axis response, varying smoothly by angle of incidence.

I'd suggest asking these questions on the sursound mailing list.

As a longtime Tetramic user, here are two basic issues I urge you to address to make the Tetramic more user friendly:

1) VVMic for TetraMic (and VVTetraVST) needs the ability to do basic A-format channel-matching gain adjustment in the standalone application.

For this very reason we recommend using a recorder (or mic pre-amps) that have digitally-set gains, so that the four channels are easily matched and don't require an external tone reference nor level matching in post. These include the Tascam DR-680, Sound Devices 788 and others.

But as you point out, this feature would be nice for the lower cost recorders that lack digitally-set gains (like the Zoom H6 and the Tascam DR2D). We'll talk about it within the TetraMic project team.

2) A small, single-box power supply eliminating the need for the four separate power supply boxes and the mess of cabling.  It should have the option of either battery or P48 powering...

Our recently introduced PPAc system provides this. The PPAc transmitter has a DC input jack so you can power TetraMic with an external battery pack instead of P48.

We've initially offered the PPAc receiver with four XLRs, for balanced output. It's simple enough to add adapters (Hosa offers them) to go from the balanced XLRs to unbalanced 1/8-inc (3.5mm).

If there's enough interest we could offer a PPAc receiver with a pair of 1/8-inch stereo plugs (unbalanced).

[Gutbucket]

Thanks, I'll ask about that on the sursound list.  Haven't payed much attention to the list for the past couple years.  I believe those types of decoders would open up previously un-tapped capabilities and provide advantages for ambisonic systems like TetraMic that are under-explored as far as I know.  I have little doubt that the researchers on that list are are way ahead of me on this conceptually.  An easy to use tool to do it is what we need.

And yes, the huge advantage of digitally set gains and the channel ganging feature which maintains the gain relationship across all 4 channels used by the TetraMic was a big factor in choosing the Tascam DR-680.  I have the raw files stored as A-format along with the calibration tones for all recordings made with the R-44, rather than the converted B-format files, simply because it was too much hassle at the time of archival to check and adjust levels before doing the B-format conversion correctly.  Those will need to be adjusted once they are revisited. 

Just as best practice, I typically store calibation tones with the TetraMic recordings made with the DR-680 files as well.  Have you found the digital gain tracking remains close enough across all channels to make doing that unecessary with the Tascam DR-680?

[Len Moskowitz (Core Sound)]

Have you found the digital gain tracking remains close enough across all channels to make doing that unecessary with the Tascam DR-680?

Yes, although there have been very rare exceptions.

[404 Not Found]

Was reading this months Pro Sound and they had an interesting article in regards to surround - side and rear ambiance added to a recording.

SoundField SPS200 Surround Sound Microphone (  http://www.prosoundnetwork.com/article/studio-review-soundfield-sps200-surround-sound-microphone-by-rob-tavaglione/18223  )

Expensive as expected, but I found interesting the software for this mic to shape the sound post recording as well as the comparing of other mic's.

Not exactly on point with the start of this thread, but interesting in re. to the capture of surround technology.

[Gutbucket]

Single point ambisonic microphones are conveneint and unbelievably flexible, great for 2-channel stereo, but IME are not ideal for optimal multichannel surround sound recording of music when used alone, as they rapidly suffer from lack of sufficient channel seperation as the channel counts increase.  They are sufficient practical solutions for less critical surround recording jobs like TV or film sound ambiances, but not for critical music listening. 


It's limited by the physics and geometry.  It's simply impossible to cram more than a few virtual first-order microphones into the same point without their patterns overlapping too much.  They are great at doing 2-channels, acceptable for 4 channels, not very good at 5 channels (requires delaying the virtual rear channels to provide sufficient diffuse decorellation), and unacceptable for more than 5.  Good live multichannel surround recording pretty much requires spacing between microphones to make up for that first-order directionality problem.  One could of course use more than one ambisonic microphone as Len mentioned previously, or use a combination of an ambisonic microphone with standard single channel microphones.