Core Sound TetraMic Ambisonic Microphone and RED

[Len M.]

Thanks to John Lizzio (#230) and his soundman Keith Kasper, we were able to test our TetraMic microphone with a brand new RED camera. TetraMic is a single-point surround-sound/stereo/ambisonic microphone.

TetraMic uses all four of RED's mic pre-amp channels; we left levels at the default gain setting. Since the camera had Build 14 installed (which disables 48 Volt phantom power), we used an external phantom power supply.

The two seem to work fine together and to be a great match.

TetraMic's recordings are post-processed to model any type of co-incident microphone array (e.g., X/Y; M/S; one or more omnis, cardioids, hypercardioids; mixes of different types of mics pointed in different directions)and essentially any playback configuration, from mono to 100+ speakers in a 3-D array. Unlike almost all other mics, it records height (vertical) information as well as the usual horizontal information.

For more information about TetraMic please visit:

http://www.core-sound.com/TetraMic/1.php

[Graeme Nattress]

Len - very cool!

Graeme

[Elizabeth Lowrey]

Will you be posting any samples?

[Kevin Halverson]

Yep, the Core Sound's TetraMic behavior is nearly identical to a Soundfield.

The ability to process the fundamental signals (X-Y-Z & W) is an excellent tool and with a nearly infinite number of configurations for various reproduction sound sources, it is highly configurable. I have been recording with Soundfield microphones for years and have achieved some remarkable results.

I would be very interested to learn your impressions of the compatibility of the TetraMic's levels when used with the RED ONE and build 14?

Kevin

[Len M.]

I would be very interested to learn your impressions of the compatibility of the TetraMic's levels when used with the RED ONE and build 14?

The default levels in Build 14 (32 dB) were fine for recording me playing an acoustic guitar and singing, with TetraMic at roughly 3-feet away.

[Len M.]

Will you be posting any samples?

I hope that either John, Keith or I will post a sound sample later this week.

If you want to hear samples of recordings made with TetraMic and other ambisonic mics, head to www.ambisonia.com. In addition to many concert recordings, John Leonard's posted a bunch of ambience recordings.

[Paul Hazlett]

what are the uses in a dialog enviroment could I pull seperate voices to
the different tracks being recorded to edit?

what about noise rejection?

this looks very interesting

[Len M.]

what are the uses in a dialog enviroment could I pull seperate voices to
the different tracks being recorded to edit?

Yes, you could configure the recording in post-processing to model one or more hypercards pointing in any arbitrary direction. You could direct each decode to its own track and in that way separate dialog based on their directions.

And you can rotate, tilt, tumble and zoom in post too. So with the right software post-processing tools, you could even track a moving sound source as if you were following it with a highly directional mic.


what about noise rejection?

I haven't thought a lot about that but in post you could place a mic pattern null pointing at the noise source.

[Paul Hazlett]

that sounds way too cool. Are you developing the software as well?

will you be at NAB?

[Len M.]

that sounds way too cool. Are you developing the software as well?

will you be at NAB?

The software is already developed. There's a stand-alone Windows application called "VVMic for TetraMic" for post-processing, and two VST plug-ins for real-time work. One plugin does the A- to B-format conversions and the other does the usual B-format to mic model/playback configuration. They are supplied with TetraMic at no additional cost.

We exhibit every year at AES. We don't expect to be at NAB. Should we be?

[Elizabeth Lowrey]

Len, all this sounds very interesting, and I will make it a point to hear some of your samples. But I'm a little curious (troubled?) that the output is not balanced. Can you comment on why such a given feature of professional microphones was not implemented here?

[Len M.]

Len, all this sounds very interesting, and I will make it a point to hear some of your samples. But I'm a little curious (troubled?) that the output is not balanced. Can you comment on why such a given feature of professional microphones was not implemented here?

The only unbalanced cable that must be used is the breakout cable. It is very well shielded and is a very short run - only one foot long. As soon as you transition to the phantom power adapter, the signal is balanced from there onwards. In practice we've found that noise pickup is not a problem.

We did it that way to keep TetraMic very small, for portable applications.

[Andrew M.]

Are you using any isolating high/low impedance transformers or the 4 unbalanced outputs are straight from the active components?

[jbeale]

Looking at the physical size of the mic, I'd bet there is no transformer in it. No good quality audio-frequency transformer could physically fit inside. If the unbalanced part is shielded and only one foot long, I doubt there would be much noise pickup.

There are shotgun microphones that have longer internal (unbalanced) cable runs than that. The same electrical principles apply.

[Steve Sherrick]

Hmmm...I'd have to give it a shot in a typical dialogue scenario and try the post processing to see what it can achieve, but it sounds interesting. Len, any issues with using the VSTs with something like a VST>RTAS plugin that I have for Pro Tools on a Mac?

Thanks,
Steve

[Dan Graetz]

For those interested here's a few pics of the TetraMic mounted on a RED. We're waiting on a few mini-XLR cables so we haven't been able to test it yet. But so far we're pretty happy with the configuration.

The 4 x PPAs tuck in nicely behind one of the side handles. Any suggestions for better setups eg. snakes, would be appreciated.

There's a thread reduction ring in the TetraMic suspension mount - into which we've screwed a Manfrotto camera stub. Next step is to try some kind of Israeli arm from the handle mount on top - to get the setup a bit higher and out of the operator's way.

Obviously we won't be running it concurrently with the Schoeps M/S setup - just trying to load the RED with as much nerdy crap as possible for the sake of a few photos :) We're also trying to work out a nice way to bolt the MixPre onto a side handle if anyone has any suggestions.

On the software side there's a VST to AU converter we're about to test. Our hope is be able to edit the ambisonics within FCP. stay tuned...

[Paul Hazlett]

can you do us a favor Graetzy and test the tetra mics ability for dialog if its not too much trouble. I would love to be able to put it on a boom and have the ability to capture audio from different people without using a wireless on everyone.

[Paul Hazlett]

We exhibit every year at AES. We don't expect to be at NAB. Should we be?

I can see alot of people who only attend NAB, like myself, being interested
in tetramic, I know of 2 very large spaces that just became available.
hehheh.

[BASSAM MSSALATIE]

TetraMic is priced at $999 is it true .?:devil:i would like to hear it's melody

[Len M.]

Are you using any isolating high/low impedance transformers or the 4 unbalanced outputs are straight from the active components?

The TetraMic's four outputs are low impedance. No transformers are used there.

[Len M.]

Len, any issues with using the VSTs with something like a VST>RTAS plugin that I have for Pro Tools on a Mac?


We don't know yet if a VST to AU converter will work. If you want to try it, let me know and we'll get you copies of the two VST plugins.

[Robert Mott]

We don't know yet if a VST to AU converter will work. If you want to try it, let me know and we'll get you copies of the two VST plugins.

We had seriously looked at buying one last summer. Knowing that it works well with the Red we are going to re-investigate.

[Len M.]

Thanks to the folks on the other audio thread, we've been able to extract the four audio tracks recorded with TetraMic and a RED camera.

In post we decoded the recording to model a Blumlein array (two figure-8 microphones positioned at 90-degrees to each other) for playback in stereo.

TetraMic was positioned only a foot or so from the RED so it picked up the RED's fan and the LCD display's whine. Next time John will hopefully have the EVF that he ordered and we'll try to remember to shut down the fan.

No EQ, compression or other processing was applied to the recording other than amplifying it +18 dB . It's a 32-bit float/48 KHz stereo recording.

Please excuse the performance -- I'm not much of a guitar player!

http://www.core-sound.com/RED/RED-with-TetraMic-Decoded-To-Blumlein2.wav

If anyone wants to see the video too, let me know and I'll see if I can post it.

Many thanks to John Lizzio and Kevin Kasper for making this demonstration possible.

[MikeHedge]

video? can you post it on youtube?

[Len M.]

video? can you post it on youtube?

At the moment, I'm using an XP/PC and can't seem to extract video no matter what I try.

RED's QT plugins are Mac-only and nothing I do with RED Cine produces a QT-viewable video.

And I haven't the slightest idea how to insert a WAV audio file into a MOV video. Perhaps Final Cut Pro will do it?

If someone wants to volunteer, I'll send them the files.

[BASSAM MSSALATIE]

Len thanks for that clip but i couldn't hear splitted audio on different channles . i hear the same audio on my 5 spurrounded speakers.
maybe it is just becuase the file format ?

[Steve Sherrick]

Len, I can add the sound to the mov file for you. PM me if you still need help with it.

[Paul Hazlett]

Thanks for posting. can you tell me the distance and position of the mic
from the subject, thanks.

[Len M.]

Len thanks for that clip but i couldn't hear splitted audio on different channles . i hear the same audio on my 5 spurrounded speakers.
maybe it is just becuase the file format ?

It's a stereo file, not a 5.1.

[Len M.]

Thanks for posting. can you tell me the distance and position of the mic
from the subject, thanks.

If I remember correctly, TetraMic was around one foot in front of the RED and two feet to the right. (John: please correct me if I'm wrong.)

The subject was seated around five feet in front of the camera. So the mic was four to five feet from the subject.

During decode, you can bring the subject in closer using the zoom control if that's what you want. For this decode, no zoom, rotation, tilt, or tumble were inserted in post. It's a simple Blumlein model with linear amplification (no compression or limiting).

[Len M.]

Len, I can add the sound to the mov file for you. PM me if you still need help with it.

Done.

[Elizabeth Lowrey]

Len, the sample has definitely piqued my interest in your product, especially given the limitations in the testing environment. Considering that you applied an 18db boost in post and that the mic was much closer to the camera than to the subject, it sounded very good with much less noise than I would expect. Will definitely hunt up the other sound samples of the tetramic you mentioned.

[Len M.]

Len, the sample has definitely piqued my interest in your product, especially given the limitations in the testing environment. Considering that you applied an 18db boost in post and that the mic was much closer to the camera than to the subject, it sounded very good with much less noise than I would expect. Will definitely hunt up the other sound samples of the tetramic you mentioned.


If you're interested I can also post a version of the Blumlein stereo decode that has been zoomed, and perhaps also a mono/hypercardioid/zoom.

[Elizabeth Lowrey]

A zoom would be great!

Quick question for you: if I'm reading the info on your site correctly, there's a breakout cable that converts the 6-pin unbalanced mic output to 4 individual mini xlr outputs, one for each capsule. However, because the tetramic requires @ 6V phantom power instead of 48, each of the 4 breakouts must also be plugged into a phantom power adapter (couldn't find pics of these on your site) to be used with standard 48v phantom sources (like most mixers, preamps, etc.) How hard would it be to simply get the RED camera to supply 6V phantom power as an alternative to 48V? Since so much about RED is firmware controlled and since it already features mini XLR inputs, I'm just wondering if a simple solution for a RED/tetramic combo could be to make a single, short breakout cable terminated in mini XLR-male that could plug directly into the 4 mini-XLR-female ports on the RED, which would then supply the appropriate 6V phantom power directly, without any intervening connectors or hardware?

[Andrew Madu]

Len,


If you're interested I can also post a version of the Blumlein stereo decode that has been zoomed, and perhaps also a mono/hypercardioid/zoom.

I would be interested in hearing you Blumlein Pair decode.

[Len M.]

Len,

I would be interested in hearing you Blumlein Pair decode.

The original file I posted was a straight Blumlein decode. Here's the link again:

http://www.core-sound.com/RED/RED-with-TetraMic-Decoded-To-Blumlein2.wav

Here's the same recording with a fully zoomed Blumlein decode:

http://www.core-sound.com/RED/RED-with-TetraMic-Decoded-To-Zoomed-Blumlein2.wav

It has the same amount of gain added as the original decode.

Here's the same recording again -- this time it's decoded to a single cardioid with mono output:

http://www.core-sound.com/RED/RED-with-TetraMic-Decoded-To-Mono-Cardioid_2.wav

[David Wilson]

Len - would it be possible to post the .amb of your fine performance? (Your guitar is better than my accordion.)

[Len M.]

...How hard would it be to simply get the RED camera to supply 6V phantom power as an alternative to 48V?

That's really a question for the RED technical folks.

From what I can guess about the design of the RED mic pre-amps, it would be a major hardware change for its phantom power circuit to generate 6 Volts instead of 48.

The TetraMic PPAs are rather small. You can see them in the pictures that Dan Graetz posted earlier.

[Elizabeth Lowrey]

The TetraMic PPAs are rather small. You can see them in the pictures that Dan Graetz posted earlier.

Looking at the XLR jack I've labeled "A", I assume the PPA is within that structure, a cylindrical part roughly twice as long as a standard XLR jack on the end of a balanced mic cable? And then the small mini XLR plug coming from the 4 X breakout cable is the part labeled "B"?

http://www.reduser.net/forum/uploaded/210_1204693649.jpg



Also, are the PPAs battery powered or do they somehow passively transform the voltage?

[Len M.]

Looking at the XLR jack I've labeled "A", I assume the PPA is within that structure, a cylindrical part roughly twice as long as a standard XLR jack on the end of a balanced mic cable? And then the small mini XLR plug coming from the 4 X breakout cable is the part labeled "B"?

That's correct.


Also, are the PPAs battery powered or do they somehow passively transform the voltage?

They operate on the 48V phantom power; no batteries are needed.

[Len M.]

Len - would it be possible to post the .amb of your fine performance? (Your guitar is better than my accordion.)

Either you're being kind or you are a really bad accordion player!

(3/18/2004 -- Link removed)

[David Wilson]

Thanks Len - I'll send you a sample of my accordion playing when I get the TetraMic/4Mic in house. Wait - I don't want that threat to slow down my deliveries...

[MikeHedge]

any news? is this working now? seem like a neat mic set up

[Elizabeth Lowrey]

I very much like the tetramic samples I've heard, both those that Len posted in this thread (recorded into RED with external preamps) and those that are in the extensive review by Paul Hodges (http://ambisonic.info/tetramic/samples.html). I will very likely get one, although probably not until after I've received my camera and played around with it some (late June, early July).

If Len happens back by this thread, I'd be interested to know how many of the early buyers have been film/video industry types. With ability to obtain hyper and super cardiod functionality in post, I'd think it would have some appeal to film sound recordists, although I think the appeal for ambient musical recordings would be much higher. Also, I wonder how close to short shotgun type isolation you can get with tetramic. I don't own a shotgun but will likely get one once I begin production on my own narrative projects and am curious if that kind of functionality can in anyway be extracted from a tetramic.

[Len M.]

I'd be interested to know how many of the early buyers have been film/video industry types.

A substantial fraction.


Also, I wonder how close to short shotgun type isolation you can get with tetramic. I don't own a shotgun but will likely get one once I begin production on my own narrative projects and am curious if that kind of functionality can in anyway be extracted from a tetramic.

TetraMic is able to model any first order microphone. That includes all mics with patterns along the continuum from omni to cardioid to supercardioid to hypercardioid to figure-8. Unfortunately, shotguns are not first order mics so they are not in TetraMic's repertoire.

[Len M.]

In previous postings we mentioned how you can record with a TetraMic and then later, in post-production, steer and zoom the microphone pattern to pick out one speaker in a group -- no boom operator needed.

Here's a You-Tube video of this being done with another Ambisonic microphone (not a TetraMic).

http://www.youtube.com/swf/l.swf?video_id=s7QrVBE5uYc&rel=1&eurl=&iurl=http%3A//i.ytimg.com/vi/s7QrVBE5uYc/default.jpg&t=OEgsToPDskLce_avdsfRwAr0FoF4JDBj

[David Wilson]

Thank you Len, amazing and potentially very useful capability.

Just to report... We've had our Tetramic for a bit over a month and absolutely love both the microphone and the astonishing spatial sense we've been able to create in the recordings made with it.

Now, with any luck, it is just a short spell before our RED arrives and we can work with these two extraordinary tools in tandem.

[Mark B.]

How does it stand up to outdoor use/inclement weather?

[David Wilson]

Mark,

We've been using the TetraMic for many months now. The mic itself is very tough. Some of the connecting parts could be considered a bit delicate just given their small size but we've had no problems at all.

The microphone itself is as rugged as any good microphone. We have used it primarily out-of-doors and have had no problems. It's vulnerability to inclement weather is, in my experience, neither greater nor less than any other microphone I have ever used.

I should say, however, that we have been doing dual system sound, not recording sound to the camera. Our camera is 2343 and we're still in line for the replacement sound board. I suspect we'll try recording directly to the camera then but suspect we will go back to dual system just because that is what we are used to.

The TetraMic itself and the remarkable world of ambisonic sound that it ushers in, we have found to be utterly superb.

Hope this helps,
David