Topic: Soundfield and Coresound Tetramic (and ambisonic mics generally)

[acidjack]

I am curious why more folks on TS.com don't seem to be experimenting with ambisonic mics like the Soundfield and Coresound Tetramic lines.

It would seem that they literally do exactly what we usually want - "record the room" - but then allow you to mix down, through software, down to virtually any pattern.  I realize some of the Soundfield mics are very expensive (the top of the line one being $6000 and requiring an extra piece of gear), but this software-based one, the SPS200, doesn't require a big piece of gear to be lugged around and seems to price out at $2700- far from cheap, but about the same as some used Schoeps, Neumanns or DPAs and much less than new ones.  I know people have their issues with Core as well, but that mic is only $1000 including the software.

I listened to some samples on the LMA from a couple of tapers down south and was pretty amazed by the spaciousness of these recordings.  Definitely a very different feel to say, a stereo pair of hypers.  I find the recordings very enjoyable to listen to - they feel very "natural" to me.

Soundfield SPS200:
http://www.archive.org/details/amt2010-04-11.stereo.flac16
http://www.archive.org/details/moe2010-03-13sps200  (this one is not as good; sounds like a boomy, echo-y venue)
http://www.archive.org/details/um2010-02-11sps200.flac.16
http://www.archive.org/details/phood2010-03-13 (decoded m/s and really nice)

Coresound Tetramic (jazz)
http://www.archive.org/details/BostonHorns2010-04-02.tetramic.flac16

Coresound Tetramic (rock)
http://www.archive.org/details/moonalice2010-03-28.tetramic.flac16

So, I assume there is a catch.  For one, there is obviously more software work involved.  I am also guessing that by nature, since the thing has mics aimed all over, it picks up a lot of chatter, so you end decoding back to hyper or something anyway a lot of the time.  I'm curious if you do so, whether the software eliminates the information that you don't want (i.e., a chatter-y channel from a mic aimed down at the crowd).   It also seems like from Soundfield's site that these are more commonly used for film rather than music.  But then, a lot of the mics we use are really designed for relatively up-close studio use, and not what we are doing, also.

I'm also curious whether placement is a difficulty - could you run one of these from a balcony just as easily as regular mics?  I tend to think so, since again, the software can presumably reject unwanted information... but I am curious.

Anyway, I would be curious to hear the opinions of those who have used these.  It seems, in theory, to be a lot easier and more versatile to just carry one mic around rather than two or even four typical SDCs.

[Brian Skalinder]

I've seriously considered the Core-Sound TetraMic solution.  All in all, it was too costly at the time, since it would have been a 2nd system only:

$      |  Description
---------------------------------------------------
  999  |  TetraMic
   65  |  6-pin extension cable, 20'
   85  |  6-pin > (4) 3-pin mini-XLR breakout cable
  240  |  (4) PPA2 phantom power adapters
   75  |  Windscreen + dead-rat
   15  |  Shipping
===================================================
1,479  |  Total

All assuming I already had a 4-ch recorder.  I wanted to maintain my main mics for running near-coincident or spaced configurations, and the TetraMic system simply proved too costly (for me) as a 2nd mic system.  There are too many instances in which I really want time-difference stereo, not just intensity-difference stereo...hence the need for 2 systems if running the TetraMic.

If I didn't care so much about -- i.e. really, really like -- time-difference stereo in such a broad array of recording scenarios, if I was happy running coincident configurations most of the time, I'd jump on a TetraMic in a heartbeat to give it a try and see what it could do.

[scb]

1st reason why I never even considered a soundfield:  it's HUGE

[illconditioned]

I might be interested in the Ambisonic mic, but I wonder about the quality of the capsules.  For all our (tapers') obsessions with expensive mics, should be take a step backward and get lower quality (*) capsules?

(*) Coresound appears to use something similar to Church Audio, or maybe Audix, capsules.  Either way, I don't expect them to be as nice as something like Scheops, DPA, AKG, Neumann, Beyerdynamic, etc. that most tapers use.  Soundfield (appears) to use MBHO (sp?) capsules.  Those are better, but maybe not enough for the discriminating recordist.

I think these mics would be great for film and other applications.  They would also be great for studio recording, like acoustic/bluegrass, where you have a great room, but may want to adjust instruments' levels in post.  But for concert recording, it seems a good ORTF, HRTF, or XY pair, would do, depending on the taper's preference.

BTW, I may still hack an ambisonic rig (with AT853 or maybe Sennheiser MKE40 capsules) but that would be just for play, not for serious recording, especially not from the taperssection at the middle or back of a large show.

  Richard

[burris]

I love my ST350, which I have had for a while but I only recently got a multitrack.  Dunno about SPS200 or Tetramic but the ST350 is a very fine mic. My Neumanns have been relegated to spot duty.  The tetrahedral mics are superior to equivalent 1st order directional mics.  It's like having directional pressure transducers with zero off axis coloration.  Everything you love about subcards but with directionality, everything you love about hypers but without bass roll off.  Plus the imaging is outstanding, you can adjust the direct and reflected ratio by ear, do ambisonic playback, etc...

The reason they aren't used more is that people don't understand them and they haven't heard what they can do.  Most people understand being able to change patterns, like mid-side on steroids, but the mics are quite a bit more than that.

Someday in the not too distant future I'm going to setup a pentagonal planar playback array.

[burris]

oh and the ST350 is small and low profile, as is the SPS200.  It would be nice if the cable connector sticking out the bottom wasn't so big, it's almost as long as the mic, but its workable.  Don't forget that a tetrahedral array recording in b-format is less fussy to setup than two mics since you don't have to choose caps/pattern, or aim, adjust angle, screw with mounts, etc...  All you have to do is get it in the right spot.

[goodcooker]

1st reason why I never even considered a soundfield:  it's HUGE

here's a pic with Dr FOB's Soundfield on a FOB tree and it's not big at all. Hardly any bigger around than a regular SD condenser and def not any longer than a AKG 460. Bigger at the top, of course, with the four capsules.

[F0CKER]

I ran the ST350 for quite some time, although I did have issues powering it and had to work through SF to get them addressed - multiple times.  The short of it, the ST350 was great if you were close to the sound source, on stage, etc..but I never really loved the sound I got from it.  It sounded a little tinny at times, the low end suffered, and seemed to be less upfront than I would prefer.  If I were recording an orchestra, jazz, on stage, nature, or something else it would be a great choice.  For a high dB rock show, it's low on my list behind virtually every other set of mics I've run, Neumann, Schoeps, AKG, Milab.  Given I spent a ton of cash on it, I REALLY wanted to love it, especially given the options recording in B format, but I think there are better options for loud PA recording, which seems to be what many of us do the most. 

[John Willett]

1st reason why I never even considered a soundfield:  it's HUGE

The SPS 200 isn't - it's like an SDC with 4 heads at the top.

[acidjack]

I agree that if the capsules are of somewhat "lower quality" than Schoeps, DPA, etc. it is potentially an issue... but I guess I would be curious what others think of the particular samples I posted.  They are all, except IMO the moe. recording, pretty great examples.   I would be more worried about the quality of Core's version than Soundfield's, I think.

Focker's comment about the mic only being good for close up an onstage is interesting, as that is kind of what I thought might be the case.  Though again, of these samples, I don't think all of them are onstage.  The moe. recording that I liked the least is clearly not. 

I am curious how mixing it down to "hyper" works... The caps are obviously pointing the way they are pointing. Let's say you have two idiots standing under your stand and the bottom-facing caps pick up a ton of those idiots.  If you mix this down to "hyper" does it somehow magically remove the idiots by rejecting the information that a hyper pointed normally *would* have rejected?  If so, that is pretty fascinating to me technologically - and also quite useful. I think many times we use hypers not because we prefer the sound, but just because we want the other qualities - rejection of off-axis noise, etc.  Having the choice would really be powerful. 

I might be interested in the Ambisonic mic, but I wonder about the quality of the capsules.  For all our (tapers') obsessions with expensive mics, should be take a step backward and get lower quality (*) capsules?

(*) Coresound appears to use something similar to Church Audio, or maybe Audix, capsules.  Either way, I don't expect them to be as nice as something like Scheops, DPA, AKG, Neumann, Beyerdynamic, etc. that most tapers use.  Soundfield (appears) to use MBHO (sp?) capsules.  Those are better, but maybe not enough for the discriminating recordist.

I think these mics would be great for film and other applications.  They would also be great for studio recording, like acoustic/bluegrass, where you have a great room, but may want to adjust instruments' levels in post.  But for concert recording, it seems a good ORTF, HRTF, or XY pair, would do, depending on the taper's preference.

BTW, I may still hack an ambisonic rig (with AT853 or maybe Sennheiser MKE40 capsules) but that would be just for play, not for serious recording, especially not from the taperssection at the middle or back of a large show.

  Richard

[martin.leese]

...
I am curious how mixing it down to "hyper" works... The caps are obviously pointing the way they are pointing. Let's say you have two idiots standing under your stand and the bottom-facing caps pick up a ton of those idiots.  If you mix this down to "hyper" does it somehow magically remove the idiots by rejecting the information that a hyper pointed normally *would* have rejected?  If so, that is pretty fascinating to me technologically - and also quite useful. I think many times we use hypers not because we prefer the sound, but just because we want the other qualities - rejection of off-axis noise, etc.  Having the choice would really be powerful. 

The way it works is conceptually easy (but, as with lots of technology, the details are not).  The outputs from the four capsules, called "A-Format", are first mixed to "B-Format".  B-Format can be thought of as an omni + three figure-of-eights pointing forward, left, and up.  If you have two figure-of-eights crossed at 90 degrees then you can rotate their responses.  With three, as described above, you can point them any which way.  And you can do this in post production.  The final bit is easy; a hyper is just the weighted sum of an omni response + a figure-of-eight response.

This means that from B-Format you can synthesize any number of hypers pointing in any direction.  And you are not limited to hypers.  By changing the weights between the omni and figure-of-eight responses, you can synthesize any response: Omni, sub, cardioid, hyper, figure-of-eight.  In fact, you can synthesize all coincident mic techniques.  And, providing you recorded the four B-Format channels, you can do it in post production.

If you want to play around, but do not have a soundfield mic, there are over 200 pieces in B-Format available for free download from http://www.sursound.com/.  B-Format can also be decoded to surround sound, and any of the pieces can also be downloaded as a DTS image that is pre-decoded for four speakers in a square.  Ad-hoc Ambisonic decoders are available for other speaker layouts (including full-sphere).

Regards,
Martin

[burris]

I am curious how mixing it down to "hyper" works... The caps are obviously pointing the way they are pointing. Let's say you have two idiots standing under your stand and the bottom-facing caps pick up a ton of those idiots.  If you mix this down to "hyper" does it somehow magically remove the idiots by rejecting the information that a hyper pointed normally *would* have rejected?  If so, that is pretty fascinating to me technologically - and also quite useful. I think many times we use hypers not because we prefer the sound, but just because we want the other qualities - rejection of off-axis noise, etc.  Having the choice would really be powerful. 

Martin covered this while I was posting, but the practical effect is you can choose the pattern, angle, and direction of your mics.  Tilt them back to face the PA or point the nulls at the audience, rotate to get perfect balance, adjust the direct/reflected ratio, etc...  Try downloading some b-format recordings from Ambisonia and get the AmbisonicStudio plugins and mess around with them.

The other thing is the b-format can be decoded into any surround format, including 3-d arrays that reproduce the soundfield where the mic was placed (room echos excepted...)

Finally, it's not just for SoundField and Core-Sound mics.  If you have two figure-8 mics and a pressure omni you can arrange them in "native b-format" which only lacks height information.  So you can rotate but not tilt the mics, and you can decode to regular surround setups.  Schoeps, of course, even makes a special mount for native b-format or double-ms (which can also be decoded to planar b-format.)   http://www.radio.uqam.ca/ambisonic/native_b.html

[martin.leese]

Forgot to mention, in addition to the mics from SoundField Limited and Core Sound LLC already mentioned, Oktava also makes a soundfield mic.  Visit http://www.oktavausa.com/ProductsPages/Ambient4DMic.html.  Finally, people have built their own tetrahedral arrays, visit http://www.ambisonia.com/wiki/index.php/Microphones#Home_made_tetrahedrons.

Regards,
Martin

[leddy]

I have a Tetramic, as well as some decent other mics (Sennheiser, Beyer, Oktava, Avenson).

My experience with it is this:  It can really sound good.  Like, spooky realism.  But...it is going to have some of the same limitations of any coincident pair.  You cannot just place it anywhere and expect to fix it all in post.  Coincident cardioids usually don't sound very spacious, so it usually needs to be decoded to something between hypers and Blumlein to reach its potential.  As such, the distance to the source is important.  You have to try to keep the source in the 90-degree recording angle as if you were using Blumlein.  Too close gives you wierd image problems, and too far gives you too much reverb.  Yes, you can fix that in post - but the further you are from proper placement usually requires fixing that by dialing out more of the rear lobes that provide the spacious sound.  You will be left with something closer to coincident cardioids.  Most of us would prefer near-coincident cards to that, I'm sure. 

In sum - think of it as a flexible Blumlein or hyper pair that lets you tweak it in post.  If you are in a situation where you would never use Blumlein or coincident hypers, you would not like an ambisonic mic either.  If you dig Blumlein or coincident hypers and know how to use them, this mic will make you very happy.  You will have much more margin of error with this than with a pair of fig. 8's or hypers.  Just not as much as with near-coincident cards.  But if it's right, it will sound way better than near-coincident cards.  Make sense?

With regard to the quality - it's all about placement.  If the mic is in the right spot, it will sound outstanding.  You will need to make no excuses. 

[gkatz]

is it correct to assume a mic like this would be great at concert with a quadraphonic system? like the pink floyd one http://taperssection.com/index.php?topic=140793.0

then playback on the same type of system, wow that would be cool.