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

[ducktaper]

after 2 decades of plowing through mic brands, the only way i'd get rid of my SF is to get another SF. Place mic and hit record, when I get home I mix. Bloom'n...if I dont like it, MS...if I dont like, hypers at 110º...if I dont like it...and so on. I have used it onstage, fob and back of the room situations. Any thought for use as a marital aid will get you slapped.

The caps are MBHO subcards but not the same used by MBHO. They are tweeked for SF but I could not get more info than that.

One mic, one cable, one recorder, one clamp...done.

[acidjack]

^^ I think it was one of your recordings that prompted me to start this thread, actually.  Great work. 

One question: From my reading, I thought the SPS200 does NOT require a computer or anything else to be brought into the field, correct?  That is, my impression is it's just as you said: mic>cable>4xXLRs>R-44 > then go home, load up the 4xWAVs into the software, and go nuts.  Is that right?

[Gutbucket]

Correct.

The output of the SPS200 & Tetramic is simply recorded in it's raw 4-channel form (called A-format).  All signal processing needed to produce usable formats (standardised ambisonic 'B-format', decoded stereo feeds, various surround formats) is done later on the computer. 

This differs from all other Soundfield mics which include a dedicated processing box which converts the A-format feed from the mic to the standarized B-format immediately, before it is recorded.  Doing it that way requres that additional dedicated hardware, but allows for real-time use of the output on-site, as well as actual monitoring while recording.  Monitoring the A-format recorded from the SPS200 or Tetramic makes sense only to check levels and for good signal (ie: checking for hum, other interference, bad connections, etc).

[edit- that means that essentially, the SPS200 and Tetramic are designed specificly for field recording and archival type applications, vs other Soundfield mics with 'realtime output' that better fit the needs of recording studios and permanent concert halls installations.]

[notlance]

Since ive been here , Ive learned a valuble , valuble lesson .
I have a ton to learn . Im just greatful that theres a place
like this to wet my appitite .

12 years later I still havn't scratched the surface... 

As far as this ambisonics stuff goes, i really like the concept.  I have been using a M/S stereo mic recently (AT4050ST).  The biggest problem with M/S is that the polar pattern is linked to width.  As you narrow the image the mic become more cardioid in polar pattern.  Thats counterproductive for many of the sources I record.  An ambisonic mic would give me controll of all of those variables in post.  I've been looking at picking up a single AT4050 to run double M/S, that seems fairly similar to this ambisonic stuff... 

Cool thread!

Yes, you can think of these mic configurations as a progression:

Mid/Side: Record two channels which allows you to vary the width in post, but changing the width also changes the virtual polar pattern.

Double M/S: Record three channels which allows you to vary the width in post with any virtual polar pattern.  However, you cannot virtually "aim" the mic.  You can, however, use this configuration to get surround sound information, as well as Blumlein.

4 cards @ 90 degrees: This configuration does not have a pithy name; maybe we could coin one.  Anyway, this 4 channel configuration allows you to decode any pattern stereo virtual mics pointed in any direction within a plane.  This is like Double M/S that can be rotated within a plane.

Ambisonics: Record four channels that allow you to have any pattern virtual stereo pair pointed in any direction.

[notlance]

Wise and true words.  I'll note that there is always an exception to the rule.  The last few years over Thanksgiving I've recorded an annual family Monopoly game at my parent's house, to document family interaction as my nieces and nephew grow up.  This year I plopped the Tetramic down in the center of the board, recorded the game with players encircling the table, then let them each take turns with the headphones listening to portions of the Blumlein decode off my laptop.  Sounded great, even the direct sounds from the out of phase regions.. I haven't listened to it on speakers though, and actual soundstage accuracy wasn't important in this case, only good upfront clarity, a nice sense of space and a differing placement of each voice.  Not a typical music gig.

Well, I have used a Blumlein configuration like you describe to record a vocal jazz group.  There were 16 singers which I assigned 4 to a quadrant around a Blumlein pair.  They were told to stay in their quadrant.  As long as they did it sounded fantastic with a very nice stereo image, and all the singers could see and hear each other very well.  This works well with a Bluegrass band too.

[RichT]

This differs from all other Soundfield mics which include a dedicated processing box which converts the A-format feed from the mic to the standarized B-format immediately, before it is recorded.  Doing it that way requres that additional dedicated hardware, but allows for real-time use of the output on-site, as well as actual monitoring while recording.  Monitoring the A-format recorded from the SPS200 or Tetramic makes sense only to check levels and for good signal (ie: checking for hum, other interference, bad connections, etc).

I've been thinking about getting either of these mics since they've become available, but the monitoring issue is too big a stumbling block for me as there doesn't seem to be any mixer or recorder which'll decode A-format.  I've used the SPS422B system though and that's great (but big and mains powered).  An ST350 would be nice, but it's too expensive.

Lots of ambisonic stuff here, including 'Native B-format' recording (on AKG Blue line- 2x Fig 8 and 1x Omni), and using Zoom H2's
http://www.radio.uqam.ca/ambisonic/

[martin.leese]

This differs from all other Soundfield mics which include a dedicated processing box which converts the A-format feed from the mic to the standarized B-format immediately, before it is recorded.  Doing it that way requres that additional dedicated hardware, but allows for real-time use of the output on-site, as well as actual monitoring while recording.  Monitoring the A-format recorded from the SPS200 or Tetramic makes sense only to check levels and for good signal (ie: checking for hum, other interference, bad connections, etc).

I've been thinking about getting either of these mics since they've become available, but the monitoring issue is too big a stumbling block for me as there doesn't seem to be any mixer or recorder which'll decode A-format.  I've used the SPS422B system though and that's great (but big and mains powered).  An ST350 would be nice, but it's too expensive.

These posts don't make any sense to me.  Of course you can do real time monitoring; any resonably modern laptop has more than enough power to do this.  And you are almost certainly going to need a laptop to record to anyway.  As for software to do this, here is what the Core Sound website at http://www.core-sound.com/TetraMic/1.php says: 

For real-time processing you would use the VVTetraVST and VVMicVST VST plugins with your recording software. VVTetraVST performs A- to B-format transformation using the calibration data for your TetraMic. VVMicVST controls virtual microphone and playback configurations. On PCs, both plugins should work with any recording application that can use VST plugins (e.g., SONAR, AudioMulch, Bidule,Wavelab, Cakewalk, Cubase, Samplitude, Ableton Live, Reason, FL Studio, Sound Forge, Nuendo, REAPER).

Many TetraMic owners hang out on the sursound e-mailing list.  Ask there to hear how people who actually own a TetraMic (which I do not) perform monitoring.  To join the sursound list visit https://mail.music.vt.edu/mailman/listinfo/sursound.

Regards,
Martin

[live2496]

I believe that you could also use Soundfield's Surround Zone VST plugin to decode to stereo for listening.

[JasonSobel]

These posts don't make any sense to me.  Of course you can do real time monitoring; any resonably modern laptop has more than enough power to do this.  And you are almost certainly going to need a laptop to record to anyway.  As for software to do this, here is what the Core Sound website at http://www.core-sound.com/TetraMic/1.php says: 

while any modern laptop would be able to use the plug-ins for real-time monitoring, I'd say that the part about needing a laptop to record is not true.  All you need is a 4 channel deck, and there are many 4-channel options these days.  Edirol R-44, Tascam DR-680, and Sound Devices 744, just to name a few.  Personally, I'd much rather take one of those decks out to record, rather than a laptop system.

[macdaddy]

Could you also use decks synced together? Like two hd-p2s, for example..?

[RichT]

Could you also use decks synced together? Like two hd-p2s, for example..?

As long as the pre's are the same.  You'll have to calibrate them with a test tone first to make sure the gains are even on all of them (this goes for 4 channel decks and laptops too).  You'll have to share the same audio clock too (which can be done on the HD-P2) to make sure they're synced

[John Willett]

I've been thinking about getting either of these mics since they've become available, but the monitoring issue is too big a stumbling block for me as there doesn't seem to be any mixer or recorder which'll decode A-format.  I've used the SPS422B system though and that's great (but big and mains powered).  An ST350 would be nice, but it's too expensive.

I have the SPS200 - If you record on a computer, the Soundfield SurroundZone software will decode the A-format and enable you to monitor.

Personally, I record on a Nagra VI and link all four mic. pres. to a single control.  I monitor only front left and right capsules to give me an idea and then sort it out in the DAW, with the Soundfield SurroundZone plug-in, later.

[Gutbucket]

I don't record to a laptop.  I record the Tetramic output to an R-44.  Since that machine has no capability of locking-down or ganging the gain settings across all 4 channels, I set everything up before a gig, calibrating gain levels to a test-tone, then checking for good clean signal with the mic connected.  I covered details on that earlier in the thread.  At the gig, I can monitor each of the four channels individually to check for good signal, noise, etc., but not for stereo image and to a lesser extent frequency balance because those things require decoding using the calibration files specific to this particular mic.  That works fine for my use, however I would prefer a recorder that allows me to match and link gains such as John does with the Nagra.

If monitoring stereo image and frequency balance is critical to you then you will need to decode the live feed in real time.  As John mentions that can be done on a laptop with the SurroundZone software for the Soundfield.  As for the Tetramic, if I recall correctly, the stand-alone VVMic software software I use to decode the recordings later only accepts input from files, not a direct soundcard input feed and so may not be useable for live decoding and monitoring.  However, I belive the VST plugin version of the software (which I have not used) should work with any recording app that supports VST plugins, four channels of input and can route the outputs appropriately.  I may be mistaken, however. 

You would want to use the VV plugin instead of the Surround Zone with a Tetramic to take advantage of the individual configuration files specific to that particular mic.

[SmokinJoe]

I've looked at these and thought about it, and I come to the conclusion "they are going to pick less of what I want, and more of what I don't want."   I'm not sure I'm correct, but that is what my engineering intuition tells me.   My only point of reference is running mid/side.  Sometimes with good success and sometimes not.

Let's say I walk up to a small stage and plan to record stage lip (Club d'Elf at the Stone Church in case anyone knows what I'm referring to).  I look ahead and there is a drum kit that is just a little too close for comfort.  There are guitars and/or bass amps either side of the drums, so it's kind of 45* left and right from straight ahead.  Later in the night a couple of drunken wookes will take up camp to the left and right of my mics.  My objective is to capture as much of those guitar amps as I can,  enough drums but not too much (too much being the problem here), and I don't want any of the drunken wookies to the left and right.


+----------------------back of stage--------------------+
|                                                       |
|                 +--------------------+                |
|                 |                    |                |
|                 |      drums         |                |
|  [guitar amp]   |                    |  [bass amp]    |
|                 +--------------------+                |
|                                                       |
|                                                       |
|                                                       |
+-------------------------- + --------------------------|
                         M/S mics   
   (wook)                                     (wook)   


It seems to me that, yes there is all this mathematical crap we can do, but fundamentally, I'm better pointing mics at what I want, rather than what I don't want.  I want those camps, I don't want too much drum and I don't want too much wook.  So why point the front of the lobe at those items I don't, and they have the guitar amps come in with off axis coloration?

Then going to the next extreme of pointing mics backwards at the wooks, I don't see how that can be beneficial at all.

One time I went to a Gov't Mule halloween show, and they were playing Pink Floyd stuff with actual surround sound channels in the back.  I wish I had run some other mics pointed backwards there... then I would have done a simple DTS5.1 mix with the front mics in the front and the back mics in the back.

[Gutbucket]

Think of this simply as an advanced, single-point coincident stereo mic with additional adjustability.  You tune the mic pattern and angles in post to optimize the situation as best as you can given your mic placement, but you can't move the mic location and there is only so much directionality available with any first order mic pattern to begin with (omni thru cardioid thru fi-8).  One of the intersting things for me in playing with decoding Tetramic recordings has been getting a better experiential, 'seat-of-the-pants' feel for that range 1st order directionality, given the coincident restriction. 

Think about it- the 1st order pattern with maximum rejection to its rear is a cardioid, and to get stereo with a coincident array you need to angle the two patterns apart.  But the more you angle them, the more you compromise the rearward rejection.  So like most things, dialing in the best decode often entails a number of compromises.  I quickly started thinking about how nice it would be to actually have something like 3rd or 5th order capability.

Forget about the capsules that point to the back.  Or rather, think of all four capsules as either adding or subtracting sound as determined by the complex matrixing that the decoding software does to synthesize the virtual microphone patterns and angles.  In that light, the rear capsules are doing their job to reduce sound to the rear of the mic, if that's how you choose to decode it, given the limitations of 1st order, coincident microphone patterns.

IMO, The best solution for the specific scenario you describe above might be seperate cardioids facing more or less straight ahead to achieve maximum rejection of the crowd, but spaced apart like an A-B spaced omni setup, which would move each mic slightly away from the center of the drum kit and closer to the guitar and bass.   I often do that with 3 or 4 omnis across the stage and the proximity of each mic to the instument sources is enough to make the level of crowd noise acceptable as 'live ambience'.  However, that's a configuration that is unavailable with a single coincident mic, ambisonic or otherwise, and pretty much the same thing applies to any near-coincident setup as well.

I have a few Tetramic recordings of Bobby Lee Rodgers in a jazz trio setting that were made in exactly the layout you describe, same proportions and angles just minus the rowdy crowd members- guitar amp(s) to the left, drums center (unamplified), acoustic bass right (bass amped through two small monitors arranged farther back on either side of the drum kit).  The Tetramic was placed just-under/in-front-of our front-center high-top table about 4'-5' from the drums and about 18" to 30" above the floor depending on the recording date.  Once I get the recordings together and converted from A to B format, I'll work on a way to share both the stereo mix-down I arrived at as well as the B-format files with anyone here who is interested, so that you can play around with the decoding yourselves using any of the the available B-format plugins.

I've been intending to make something like this available, but it will take some time to get together.