Topic: Core Sound TETRA Questions for LEN

[Nick's Picks]

your retail post is locked, so i can't ask there.

1.  4 channel output via a custom cable, probably 5 or 7pin > 4x male XLR ?
2.  is there an "outboard" controller box to select polar patterns, provide phantom ?
3.  will it operate in any mode other than "A format" ?
4.  does it come w/bundled software so that you can actually do something w/the files ?

Basically...
lets say I'm joe taper.  I want to buy this mic and use it in the field.
what do I need to go from "in the field" to "in the living room" mixed down two channel stereo ?

would I need something like an R4 w/4 channels of preamp / phantom ?

this product looks really cool, and i'd love to get my hands on one.  but there are a lot of holes in the marketing, almost like you expect the end user to know what they need to do w/this microphone.
Its very intriguing, but mysterious.  Can you provide a list of materials one would need to use one of these for concert taping ?

[Nick's Picks]

I answered a few of my own questions by reading the site.

it comes w/the appropriate software ?  not sure on that.  it comes w/something, but I dont know if its the entire package or just a plugin for something else.

it works w/the Core-Sound "4mic" preamp/AD...which isn't shipping ?
will it work w/any 4 channel recorder ?

[WiFiJeff]

I have to admit to being totally pissed off a month ago when I attempted to learn something useful about this system.  Even though I have dropped a lot of cash over the years with Core Sound (several sets of mics, including two high-end binaurals, one configured for the Mic2496 and PDA system I could never get to work reliably, a Jecklin disk, cables, etc.) I was treated by Len more like an industial spy than a prospective customer.  Since no response curves for the mics are given, and the claimed response range is limited to below 18.5 kH, I was concerned whether the drop-off was smooth or abrupt.  The type of mic used is being treated as a deep secret, though I am told that, by inspection, lots of guys have IDed it as a common Chinese cap.  Len's reaction to my question on hf response was "How old are you?" I guess implying I couldn't hear that high any-old-how (this from a guy selling 24/96 gear, yet).  So when I make the move to surround, it's going to be Soundfield or Josephson C700S, even if they cost five times as much.  At least I'll have some confidence I'm getting something useful.

Jeff

[boojum]

"Everyone knocks stones from a crumbling wall."  I had trouble with Len, too.  I asked him about a set of expensive mics and he never took the time to respond.  So I bought them from Sweetwave, who treated me very nicely.  I cannot be bothered with retailers on the Internet who cannot answer their e-mails.  Too many good companies do.   YMMV   

[illconditioned]

I have to admit to being totally pissed off a month ago when I attempted to learn something useful about this system.  Even though I have dropped a lot of cash over the years with Core Sound (several sets of mics, including two high-end binaurals, one configured for the Mic2496 and PDA system I could never get to work reliably, a Jecklin disk, cables, etc.) I was treated by Len more like an industial spy than a prospective customer.  Since no response curves for the mics are given, and the claimed response range is limited to below 18.5 kH, I was concerned whether the drop-off was smooth or abrupt.  The type of mic used is being treated as a deep secret, though I am told that, by inspection, lots of guys have IDed it as a common Chinese cap.  Len's reaction to my question on hf response was "How old are you?" I guess implying I couldn't hear that high any-old-how (this from a guy selling 24/96 gear, yet).  So when I make the move to surround, it's going to be Soundfield or Josephson C700S, even if they cost five times as much.  At least I'll have some confidence I'm getting something useful.

Jeff

I'm guessing the capsules are similar to what Chris Church is using.  I do in fact know a source of these, but I'm not disclosing out of respect for Chris.  My opinion: this is a great budget-priced, utility-grade capsule, but I would not trust them for high end imaging market the tetramic is aiming for.  Until someone (Core sound, or otherwise) discloses the capsule type and/or detailed specs (and all the other stuff people are asking about actually using the mic!) I wouldn't spend any money on this stuff.  I mean we are spending big money, we should at least get some technical information.

IMO "Joe taper" is probably going to be much happier with, either a pair of Neumanns or Beyers, or, I guess an MS setup, however that is achieved.

I've considered building an ambisonic mic, but if I did, I would probably build from the Sennheiser MKE40 capsules.  It might would be more expensive to build, and it would probably need some EQ to improve the LF response, but I do like that capsule for the level of detail.

A final question concerns patent issues.  Is the Soundfield patent still active?  Is tetramic violating patent?

  Richard

[Mr.Fantasy]

A final question concerns patent issues.  Is the Soundfield patent still active?  Is tetramic violating patent?

Tune in next time...same bat time, same bat station....

[DSatz]

WiFiJeff, I don't wish to defend anyone's bad attitude, but by itself a rolloff in a microphone starting at 18.5 kHz is little cause for concern. Some of the ribbon mikes that some people think are so f'ing great roll off starting at 7 kHz, and you might be amazed to see the actual high-frequency response of some very highly regarded studio condenser microphones (particularly off-axis) as opposed to their published spec-sheet curves.

But as I said this is little cause for concern since at such high frequencies, there is rarely any significant sound energy even in "acoustic" music at normal recording distances--and if you record amplified music, forget it--there's essentially none at all.

You remarked on the fact that this person sells 24/96 kHz equipment. For the past five years or more it has become impossible to market any digital recording system that doesn't support at least 96 kHz. But the point of it was never to capture higher frequencies than 44.1 kHz can record; it was to capture the audible range more accurately. Any PCM audio system requires low-pass filters to exclude any frequencies at or above one-half the sampling rate. A sampling rate of 44.1 kHz, while objectively adequate for all frequencies audible to humans, leaves only the very small interval between 20 kHz and 22.05 kHz for this filtering to take effect.

The main justification for 96 kHz recording, such as it is, is to allow those filters to begin their effect higher in frequency (above 20 kHz) and to have gentler slopes. This allows for flat frequency response to 20 kHz plus better impulse response in the audible range, both of which can be measured and occasionally even heard by some people on some material when listening on electrostatic headphones--though not by most people on most material, and certainly not on any normal home loudspeaker systems.

Please pardon me if you already knew all this; I'm just trying to contribute a little perspective. I might have been interested in that system as well, except that having great versatility in processing the signals from crappy capsules ultimately isn't going to produce any results to get excited about. It was always the problem with the original Soundfield system (I'm thinking 20+ years ago) that its Calrec capsules just weren't really very good sounding, though I understand that the more recent ones are quite a bit better. Still, I have no use whatsoever for height information in a recording, and would rather use a mike with three really good capsules and correspondingly simpler processing.

--best regards

[udo]

I believe a double ms setup with three really good microphones and a 4-track recorder (modded R4) will bring much, much better result. But then again a 2 Schoeps CCM4 and a CCM8 + the Rycote suspension cost you BIG money, but you will at least have sound that is as good as the schoeps stereo recordings. And for music recordings: we need to record only two dimensional, there is not too much sound coming from the sky (or the ceiling ...) usually.
On this site you will see someone experimenting with a self-made surround sound version ...
http://www.uwm.edu/~type/audio-reports/QuadPacConstruction/index.html
I believe there are many ways to experiment with different (and cheaper) microphones then schoeps. The tetra mic reminds me a bit of the first compact-stereo systems, which were marketed as the great thing, everything included, but the sound is poor.

[live2496]

Perhaps we will hear from Len soon, but I can fill you in on what I know about it.

You need to record to discrete tracks and then run the audio through a post conversion process to convert into B-format. Once in b-format, there is software that can decode the ambisonic b-format file into multiple speaker feeds depending upon your speaker configuration.

Each microphone needs calibration to account for differences in capsules.

This is probably the most advanced software to date here...
http://www.kokkinizita.net/linuxaudio/tetra-pict.html

It's a linux software for calibration of the tetramic and conversion of a-format to b-format.

This is a new area for software development. Another person is developing plugins for OSX.
The best source for information I think is the wiki on www.ambisonia.com.

A number of decoders are available. One for windows is called VVMIC, but there are others. There is a java based player also. Some of this information I posted in Teddy's thread about Audio Reference.

edit: apparently the VVMIC developer has plugins also available for windows. These are VST plugins that should work in an windows recording app that supports VST. This makes it possible to encode to b-format while recording.

[Nick's Picks]

ok, so you record 4 raw channels of A format.
then you need to convert that to B format, which has been around for a while and there are software packages out there (just like for the soundfields), and from there you can do all your picking/chooseing w/the angles and polar patterns.

those capsules looked at first like Audix.
whatever they are, I wonder if they sound any better than Oktava mk-012 version of this array.

one thing I dont like is the look of this mic.  Its small, thats cool.  But it looks like something I used to clean my bong with.

I saw one pictured in a stereophile magazine recently (as they were doing some recording and documenting it).  they were not using it, it seems Len was there and they just snapped a pic of it.

Still...
Len, if you want a review on nickspicks.com.  get a kit together for me consisting of the mic and the 4mic box (if that's what you recommend) and let me see if this sucker is going to rock the taper world...., or just be a stack of paper (precision) weights.  I'd love to give it a fair go.
 

[Church-Audio]

I have to admit to being totally pissed off a month ago when I attempted to learn something useful about this system.  Even though I have dropped a lot of cash over the years with Core Sound (several sets of mics, including two high-end binaurals, one configured for the Mic2496 and PDA system I could never get to work reliably, a Jecklin disk, cables, etc.) I was treated by Len more like an industial spy than a prospective customer.  Since no response curves for the mics are given, and the claimed response range is limited to below 18.5 kH, I was concerned whether the drop-off was smooth or abrupt.  The type of mic used is being treated as a deep secret, though I am told that, by inspection, lots of guys have IDed it as a common Chinese cap.  Len's reaction to my question on hf response was "How old are you?" I guess implying I couldn't hear that high any-old-how (this from a guy selling 24/96 gear, yet).  So when I make the move to surround, it's going to be Soundfield or Josephson C700S, even if they cost five times as much.  At least I'll have some confidence I'm getting something useful.

Jeff

I'm guessing the capsules are similar to what Chris Church is using.  I do in fact know a source of these, but I'm not disclosing out of respect for Chris.  My opinion: this is a great budget-priced, utility-grade capsule, but I would not trust them for high end imaging market the tetramic is aiming for.  Until someone (Core sound, or otherwise) discloses the capsule type and/or detailed specs (and all the other stuff people are asking about actually using the mic!) I wouldn't spend any money on this stuff.  I mean we are spending big money, we should at least get some technical information.

IMO "Joe taper" is probably going to be much happier with, either a pair of Neumanns or Beyers, or, I guess an MS setup, however that is achieved.

I've considered building an ambisonic mic, but if I did, I would probably build from the Sennheiser MKE40 capsules.  It might would be more expensive to build, and it would probably need some EQ to improve the LF response, but I do like that capsule for the level of detail.

A final question concerns patent issues.  Is the Soundfield patent still active?  Is tetramic violating patent?

  Richard

I am using the same capsule. But I modify mine in a few different ways to bring out the performance. I dont know what Len does to his capsule but as them come stock they are not much to cheer about.  And I carefully hand match all of my capsules to 0.04 db max of each other. As ones from the same batch can be off by as much as 6 db from each other I buy large amounts and find good matches. They are a good sounding capsule once you do a few things too them. 

[WiFiJeff]

WiFiJeff, I don't wish to defend anyone's bad attitude, but by itself a rolloff in a microphone starting at 18.5 kHz is little cause for concern.

I understand.  But would you spend $1000 on a mic with no polar or frequency charts (however misleading those may at times be), using a mysteriously-sourced capsule, and no other info?  It's not like I was offered a better package of specs or comparisons.  

You remarked on the fact that this person sells 24/96 kHz equipment. For the past five years or more it has become impossible to market any digital recording system that doesn't support at least 96 kHz.

He was an early adopter of this marketing ploy.  I bought the PDA-Audio stuff as soon as it was out, only to have the first six months go by as a nightmare beta test since almost nobody was able to get a system to run at 24/96, some of the original gear and software that was supposed to make it run just couldn't.  By the time the software and PDAs that would work were becoming useable there were better smaller more reliable options available.

This allows for flat frequency response to 20 kHz plus better impulse response in the audible range, both of which can be measured and occasionally even heard by some people on some material when listening on electrostatic headphones--though not by most people on most material, and certainly not on any normal home loudspeaker systems.

I use the Stax electrostatics, a superb system.  Makes it hard to listen to any loudspeaker playback.

Please pardon me if you already knew all this; I'm just trying to contribute a little perspective. I might have been interested in that system as well, except that having great versatility in processing the signals from crappy capsules ultimately isn't going to produce any results to get excited about. It was always the problem with the original Soundfield system (I'm thinking 20+ years ago) that its Calrec capsules just weren't really very good sounding, though I understand that the more recent ones are quite a bit better. Still, I have no use whatsoever for height information in a recording, and would rather use a mike with three really good capsules and correspondingly simpler processing.

Your input as usual is very helpful.  I am leaning to the Josephson C700S just for these reasons.  

Jeff

[muj]

[/quote]

Your input as usual is very helpful.  I am leaning to the Josephson C700S just for these reasons.  

Jeff


[/quote]




If you buy that mic I'll kiss your feet

[DSatz]

WiFiJeff, I haven't dealt with Core Sound enough to have an opinion about the service or the attitude, but I do know David Josephson--he's one of my personal heroes in the audio profession. I sometimes wish I had a good excuse to buy something from him. You can count on his honesty and sincerity, as well as a good deal more knowledge and common sense than a lot of other people who promote their supposed expertise in this field.

--best regards

P.S.: I haven't heard Stax Electrostatics in almost 35 years now, but used to have a pair of SR-X phones and one other model of theirs, plus a little tube amplifier to drive them. They sounded too good, was the problem--if I made a so-so recording, it would still sound good through those headphones.

As a musician I learned to practice in a room that made me sound bad until I could sound good in that room--then I'd be ready to sound good almost anywhere. Same thing with live recording--if a playback system coats everything with sugar, let me save that for when I do playbacks for certain clients, but for my own criticial listening I want the most neutral sound possible. Headphonewise, for me that would be something more like Koss electrostatics, though again headphone listening is fundamentally deceptive and inadequate; if I'm recording primarily for loudspeaker playback (i.e. all the time, practically speaking), I need to monitor over loudspeakers to know what I'm doing.

[Nick's Picks]

if only those c42s of his were not so bright...i'd be all over a pair.

[J.T.L]

...so I guess Core Sound is not interested in giving us details on this mic?

[Nick's Picks]

I got email from him directly as he seems to have bad luck posting here w/o the trolls / flamers kicking his asci all over the place.

you need the 4mic thingy..which isn't available.
or you need a 4 channel recorder w/4 preamps (R4, or higher end.  744 wont do).

comes w/software...but not sure if its everything you need to process from 4 channel A > B > stereo.

Overall, after my discussions w/him it seems this thing is just not user friendly.  maybe i'm wrong, and w/all the tools in hand to use it it might be a pleasure.   I'm hoping that once everything falls into place at CS, that he'll send me a unit w/the 4mic for review.
I'll even give you a CC# Len.


as for details of the mic....
WYSIWYG, and thats all i know.

[live2496]

Here is some information posted by Paul Hodges who was one of the early recipients of the Tetramic.
http://www.ambisonic.info/tetramic/

Gordon

[mkoijn]

Hi, My first post. I'm building an ambisonic mic, it's not finished yet, but have a look at it here

http://www.violini.de/

I think the capsules I'm using are identical to Coresounds capsules for the following reasons. On their website it shows as the main pic what is probably one of their earliest mics, you can see that the capsules are in three pieces, there is a narrow section right at the top. In other pics of their mics, the thin top secion is missing, that is, the two sections, the top and the bit with the holes, are now one piece. On the website of the supplier where I bought my capsules, it shows the capsules as being in 3 pieces, When I received my capsules however, they are in two pieces.... The manufacturer has obviously cut costs, and is now supplying two piece capsules, which coresound are also using. Too much of a cooincidence.

[illconditioned]

Hi, My first post. I'm building an ambisonic mic, it's not finished yet, but have a look at it here

http://www.violini.de/

I think the capsules I'm using are identical to Coresounds capsules for the following reasons. On their website it shows as the main pic what is probably one of their earliest mics, you can see that the capsules are in three pieces, there is a narrow section right at the top. In other pics of their mics, the thin top secion is missing, that is, the two sections, the top and the bit with the holes, are now one piece. On the website of the supplier where I bought my capsules, it shows the capsules as being in 3 pieces, When I received my capsules however, they are in two pieces.... The manufacturer has obviously cut costs, and is now supplying two piece capsules, which coresound are also using. Too much of a cooincidence.

Very nice metal work.  You're not a plumber by any chance, are you, lol!

Nice to see people building gear, and even nicer to see *mechanical* contraptions, something I could never achieve.

Question: are those brass or copper fitting you're using.  I'm not sure, but you *may* have to worry if you've got two different metals involved.  I think the capsules themselves are brass I think.

  Richard

[Nick's Picks]

so as I look at these "tetra" style mics, I see that the deal is its a cheap form of the soundfield array.  Even their new A format mic is basically the same..
but what is the difference between B and A format ?
also, the Soundfield MK/ST series, the diaphragm is mounted where the actual capsules would be "screwed in" if you were using pre-bought caps.  Does that difference in capsule distance matter ?

[jerryfreak]

+T, nice work!

Hi, My first post. I'm building an ambisonic mic, it's not finished yet, but have a look at it here

http://www.violini.de/

I think the capsules I'm using are identical to Coresounds capsules for the following reasons. On their website it shows as the main pic what is probably one of their earliest mics, you can see that the capsules are in three pieces, there is a narrow section right at the top. In other pics of their mics, the thin top secion is missing, that is, the two sections, the top and the bit with the holes, are now one piece. On the website of the supplier where I bought my capsules, it shows the capsules as being in 3 pieces, When I received my capsules however, they are in two pieces.... The manufacturer has obviously cut costs, and is now supplying two piece capsules, which coresound are also using. Too much of a cooincidence.

[mkoijn]

@Illconditioned,

The construction is all brass, I hope there won't be problems

@jerryfreak, Thank you!


I do believe that to build an ambisonic mic for the price that Coresound sells theirs for, they would have to use fairly cheap capsules given the amount of calibration required for each individual capsule plus the calibration of the array of capsules together to get the B-format correction files. Thats a lot of work plus the hardware and electronics and they still have to make a profit too.  I think they must have put in a lot of work to sort out the calibration problems. So I don't think they are ripping anyone off, just because they possibly use cheaper capsules.

From the few recordings made with the Tetramic that are available  on the internet, it seems a very neutral kind of mic, which is exactly what i'm looking for.

Regards

Albert

[Nick's Picks]

yes, I've also been admiring the brass work.
very nice.

[wbrisette]

edit: apparently the VVMIC developer has plugins also available for windows. These are VST plugins that should work in an windows recording app that supports VST. This makes it possible to encode to b-format while recording.

As it turns out, I know the guy developing the software for Len. I went to High School with him and worked with him during HS. I spoke with him the other day. He told me he has a Mic Len sent him. We talked about getting together, so if that happens, I'll see how well it works with the Deva.

Wayne

[mkoijn]

@Moke,

The capsules come as a two part piece, the diaphragm in the upper part, and the built in fet circuit(which is removable) in the smaller lower section. The two sections can be unscrewed. I simply unscrewed the lower halves, removed the fet circuit board, sanded the paint off, then filed 3 angles on each. My wife then held them with tweezers in turn whilst I spot soldered it all together. The fet circuits still fit where they used to and the top sections just screw staight back on as in the pics. I may replace the fets, as someone on another forum said they are quite noisy. I will experiment.

Best regards and thanks for the compliments, I will try to post a clip and more photos when it's finished.

Albert

[Gutbucket]

so as I look at these "tetra" style mics, I see that the deal is its a cheap form of the soundfield array.  Even their new A format mic is basically the same..
but what is the difference between B and A format ?

A-format is the raw feeds from a mic with caps in the 'tetra' form.  It is un-corrected and specific to each mic. (imagine the signals output by capsule position- ie: upper front left, lower front right, lower back left, upper back right). In most ambisonic mics (like the Soundfields) it is converted to B-format by the mic itself or its processing box before recording.  In Len's mic it is not, and the raw A-format signal is recorded.  That allows him to eliminate the processing hardware and do the conversion later digitally.  It also means you can not monitor or listen to the recording until it is decoded later.

B-format is the basic universal ambisonic format.  This is what you need to 'do something' with the recording like adjust, mix, decode to different stereo or surround formats, etc.  Ambisonic 1st order B-format signals are the mathmatical equivalent of and omni and three fig-8 mics, one pointing left, one forward, one up, all of them located in the same point.  (W,X,Y,Z)  If you were to set up some coincident figure-8's and an omni and recorded the output you would be recording 'native B-format'.

also, the Soundfield MK/ST series, the diaphragm is mounted where the actual capsules would be "screwed in" if you were using pre-bought caps.  Does that difference in capsule distance matter ?

Yes it does, and that's one of the reasons that the 'tetra' mic form (and the hassle of dealing with A-fomat) is a popular design choice for an ambisonic mic.  The 'tetra' form gets the capsules much closer to truely coincidet than you could by arranging three figure eights and an omni (it's also less expensive to use four cardioid capsules to build the mic).  Even so, It's still not close enough, so there is some high frequency correction that is usually done along with the A to B format conversion that helps compensate for the non-coincidence somewhat. 

Conceptually, this whole ambisonic thing is an extension of M/S recording.  Think of it as starting with a pair of fig-8's arranged for M/S and adding another fig-8 (pointing up) and an omni.  The rest is matrix tricks just like decoding M/S. 

In this light, consider that the design problems in adpting a 'tetra' style arangement for a ambisonic mic is similar in nature though more complex to those encountered when trying to create a figure-8 pattern by using two opposing cardioid mics and flipping the polarity on one of them.

[Gutbucket]

@Moke,

The capsules come as a two part piece, the diaphragm in the upper part, and the built in fet circuit(which is removable) in the smaller lower section. The two sections can be unscrewed. I simply unscrewed the lower halves, removed the fet circuit board, sanded the paint off, then filed 3 angles on each. My wife then held them with tweezers in turn whilst I spot soldered it all together. The fet circuits still fit where they used to and the top sections just screw staight back on as in the pics. I may replace the fets, as someone on another forum said they are quite noisy. I will experiment.

Best regards and thanks for the compliments, I will try to post a clip and more photos when it's finished.

Albert

Great idea and fine work.  That's an ingenious and beautifully simple construction method, especially since everything still fit after filing the angles on the capsule bodies.  Even bigger congratulations on finding such a wife!

[mkoijn]

Great idea and fine work.  That's an ingenious and beautifully simple construction method, especially since everything still fit after filing the angles on the capsule bodies.  Even bigger congratulations on finding such a wife!

Yeah, she's a little treasure, she is going to recorded with it the new mic though. 

[live2496]

Hugh Pyle recorded this jazz group using a tetramic and an RME Fireface.
The recordings were converted to UHJ for stereo listening using some software that Hugh developed. I don't really know anything about the software right now.

A very nice stereo field if you want to take time to listen.

http://www.myspace.com/soulforcev

This should give some kind of idea of what kind of sound can be obtained with the tetramic.

Gordon

[boojum]

Interesting.  Thanks for the posted link.

[Church-Audio]

I will be selling 4 matched capsules and the tube necessary to build these mics if anyone wants to build there own I can supply it with a 4 ch battery box and 4 matching capsules  for $300 cabling will be extra if needed. The tube will be precut lengths that you can jerryrig into a array. I dont want to get into building the arrays but I will supply the parts to do so. You will need software to convert the program material.

[hugh]

Hi folks.  To follow up on Gordon's link with a bit more detail of my chain and that particular recording:

This was recorded at Zoe's, a tapas bar in Beverly Farms, MA, which has really nice acoustics -- their ceiling is curved and finished with acoustic treatment.  The band is bass, drums, guitar (small amp on the floor), saxophone (not mic'd), and vocal.  The mic was suspended upside-down from a boom, quite close to the band.  Recording chain is: TetraMic, to a Daking Mic-Pre IV (my favorite toy!), then FireFace 800 for A/D conversion, then a laptop running AudioMulch (48kHz, with a four-channel file writer at 24 bits, and the RN Digital Inspector VST spectrum analyzer and peak meter).  The original recording is A-format, which I then adjust to pre-measured gains of my mic pre's four channels, then converted to B-format using the VVMic software supplied with TetraMic, then mixed down to stereo.  (The A-format calibration and B-to-stereo downmix software are my own: http://cabezal.com/~inguz/stuff/AFormat.zip).

I usually mix things down to crossed-hypercardioids for stereo.  But this set, the mic was really too close to the band: sax way over the left side, and vocal PA almost 180 degrees the opposite side; crossed-mic mixes sounded really weird and unbalanced, and phasey when the sax player moved around.  So I played around for a long while trying to get the right mix: rotating the microphones, trying different directivities from cardioid through figure-eight, even tilting up, down and sideways.  And finally settled on the UHJ mix, which keeps a really nice balance of reverb and ambience, but brings the sides in toward the front.  Downside of UHJ is that it usually sounds quite "distant", even for classical orchestra.

So that's one amazing thing about recording with TetraMic.  You really can throw up a mic just about anywhere that sounds good -- even upside-down, as here, or pointed straight at the door, or whatever -- and play around with complete freedom in rotating and mixing to stereo later.  And I think the results are good: incredibly stable and solid stereo image.  (There is a little "wandering" on the Zoe's tapes, but that's actually due to using Audacity's default compressor instead of SC4.  But these tracks really aren't much compressed at all).

Hugh

[F0CKER]

^ one of the reasons I keep fighting through my Soundfield issues.

The flexibility is awesome. 

[illconditioned]

I will be selling 4 matched capsules and the tube necessary to build these mics if anyone wants to build there own I can supply it with a 4 ch battery box and 4 matching capsules  for $300 cabling will be extra if needed. The tube will be precut lengths that you can jerryrig into a array. I dont want to get into building the arrays but I will supply the parts to do so. You will need software to convert the program material.

I'm interested in hearing more about this, Chris.

Can you post a picture of the "tube" that you refer to?

  Richard

[Church-Audio]

I will be selling 4 matched capsules and the tube necessary to build these mics if anyone wants to build there own I can supply it with a 4 ch battery box and 4 matching capsules  for $300 cabling will be extra if needed. The tube will be precut lengths that you can jerryrig into a array. I dont want to get into building the arrays but I will supply the parts to do so. You will need software to convert the program material.

I'm interested in hearing more about this, Chris.

Can you post a picture of the "tube" that you refer to?

  Richard

Its just 4 pcs of brass tube that can be joined or welded into a tetrahedral mount. Some machining would be required.

Chris

[live2496]

The original recording is A-format, which I then adjust to pre-measured gains of my mic pre's four channels, then converted to B-format using the VVMic software supplied with TetraMic, then mixed down to stereo.  (The A-format calibration and B-to-stereo downmix software are my own: http://cabezal.com/~inguz/stuff/AFormat.zip).

Hugh,
Thanks for providing the details. Can you tell us more about how you go about setting your levels?

Gordon

[hugh]

I generally look at the RNDigital plugin during a soundcheck -- it has nice resettable peak displays -- and aim to be around -9dBFS at peaks.  Real performance always peaks at least 3dB louder than soundcheck in my experience!  Occasionally of course I miscalculate and need to pull the gains down during a track break.  With 24-bit recording I feel comfortable recording some distance away from peak; the noise floor is pretty low.

The pre I use doesn't have ganged gain across the channels (an advantage of units like the MOTU Traveler) but it does have stepped gain controls instead of potentiometers, and I've measured them fairly well: channels are matched within about 0.3dB (and I calibrate afterward to adjust for that), but channel gain matching doesn't vary significantly at all with the actual gain setting.

[SparkE!]

I will be selling 4 matched capsules and the tube necessary to build these mics if anyone wants to build there own I can supply it with a 4 ch battery box and 4 matching capsules  for $300 cabling will be extra if needed. The tube will be precut lengths that you can jerryrig into a array. I dont want to get into building the arrays but I will supply the parts to do so. You will need software to convert the program material.

I'm interested in hearing more about this, Chris.

Can you post a picture of the "tube" that you refer to?

  Richard

Its just 4 pcs of brass tube that can be joined or welded into a tetrahedral mount. Some machining would be required.

Chris

The angle between any two adjacent mics would be about 109 degrees.  So, to make the tubes meet correctly, you'd make 3 marks, equally spaced circumferentially around each tube and use those marks to help you align 3 cuts, each approximately 109/2=54.5 degrees to the axis of the tube.  It's probably easier to avoid the machining of the tubes and simply drill 4 holes of the correct diameter into the center of each face of a tetrahedral block and then just glue the tubes into the holes.  Of course, then you have to machine a tetrahedral block.  Adjacent faces of the block are about 71 degrees from each other.  On second thought... This doesn't look too easy to me.

[Church-Audio]

I will be selling 4 matched capsules and the tube necessary to build these mics if anyone wants to build there own I can supply it with a 4 ch battery box and 4 matching capsules  for $300 cabling will be extra if needed. The tube will be precut lengths that you can jerryrig into a array. I dont want to get into building the arrays but I will supply the parts to do so. You will need software to convert the program material.

I'm interested in hearing more about this, Chris.

Can you post a picture of the "tube" that you refer to?

  Richard

Its just 4 pcs of brass tube that can be joined or welded into a tetrahedral mount. Some machining would be required.

Chris

The angle between any two adjacent mics would be about 109 degrees.  So, to make the tubes meet correctly, you'd make 3 marks, equally spaced circumferentially around each tube and use those marks to help you align 3 cuts, each approximately 109/2=54.5 degrees to the axis of the tube.  It's probably easier to avoid the machining of the tubes and simply drill 4 holes of the correct diameter into the center of each face of a tetrahedral block and then just glue the tubes into the holes.  Of course, then you have to machine a tetrahedral block.  Adjacent faces of the block are about 71 degrees from each other.  On second thought... This doesn't look too easy to me.

I dont remember saying it was easy but it can be done.

[Gutbucket]

One simple method that comes to mind if you have access to a standing belt-sander machine:
Make a simple jig to hold the brass tube square to the sanding surface and mark the rotation of the tube. Set the sander table angle to make a 54.5deg with the belt.  Sand one angle, rotate tube 120deg, sand second angle, rotate tube 120deg sand third angle.  Repeat with the other three tubes.

Might be easier to epoxy the angled tube ends together.  It's mighty tricky to hold those pieces in place while the solder or braze flows.  If you do one and then try to add a second, the first joint will melt - a big part of what makes Albert's tube soldering work so impressive.  You really need to hold them all in place and do them all at once.

[live2496]

I generally look at the RNDigital plugin during a soundcheck -- it has nice resettable peak displays -- and aim to be around -9dBFS at peaks.  Real performance always peaks at least 3dB louder than soundcheck in my experience!  Occasionally of course I miscalculate and need to pull the gains down during a track break.  With 24-bit recording I feel comfortable recording some distance away from peak; the noise floor is pretty low.

The pre I use doesn't have ganged gain across the channels (an advantage of units like the MOTU Traveler) but it does have stepped gain controls instead of potentiometers, and I've measured them fairly well: channels are matched within about 0.3dB (and I calibrate afterward to adjust for that), but channel gain matching doesn't vary significantly at all with the actual gain setting.

Taking a look at the console programs...
So if I had 4 unmatched levels, I could record a test tone and the software will adjust the gain?
Could you describe the recording of the test tones? Do you record at 4 compass points, or what steps are involved in this process?
And is this 4 mono wav files or 1 interleaved file?

C:\Hugh Pyle>aformat
A-Format file analysis and normalization.

Assuming several channels of audio, each with a calibration
tone of several seconds near the start or end of the track.
Scans the file for 1-second regions where the signal is
greater than -40dB and very constant (lowest standard
deviation of the Hilbert envelope).  Typical deviations
with well-recorded calibration tones will be less than 0.05dB.

Reports the relative gains of these calibration signals and
optionally normalizes the file(s) by amplifying each channel
to the gain of the loudest calibration signal (producing 32f WAV).

Usage:
AFormat <infile> [/output <outfile>] [/gain n] [/cal n] [/test n] [/testmin n]

  <infile> (input filename, or * for all WAV files in the current folder)

  Optional:
  /output <outfile> (output filename)
    (use '-' for stdout)
    (if not specified, only gain coefficients are calculated)
    (if input is '*', this is the 'base' output filename)
  /gain <n> (dB; defaults to 0)
  /cal <n> (seconds to scan for calibration signals; defaults to 60)
    (negative values seek from the end of the file)
    (or use a filename if calibration signals are separate)
  /test <n> (seconds of cal signal to look for, defaults to 1)
  /threshold <n> (dB, defaults to -40)

[hugh]

The test tones are to take the same input, through each channel of the pre/convertor, to measure those channels in turn.  For my pre, I did this acoustically: with a single microphone near a loudspeaker playing a sine tone, plugging the mic into each channel one at a time while recording the outputs.  (Then for convenience I aligned the channels in Audacity, since the whitespace isn't useful).  The result for my pre is here: http://halfbricking.com/Samples/daking.wav

Then: AFormat /input <aformat_recording.wav> /output <aformat_calibrated.wav> /cal daking.wav

[hugh]

Hey, another stereo sample: http://halfbricking.com/Samples/sample_WhenWeCome_1644.wav

(Full surround version here: http://www.ambisonia.com/Members/hughpyle/ambisonicfile.2008-10-20.9949056803/)

[live2496]

The test tones are to take the same input, through each channel of the pre/convertor, to measure those channels in turn.  For my pre, I did this acoustically: with a single microphone near a loudspeaker playing a sine tone, plugging the mic into each channel one at a time while recording the outputs.  (Then for convenience I aligned the channels in Audacity, since the whitespace isn't useful).  The result for my pre is here: http://halfbricking.com/Samples/daking.wav

Then: AFormat /input <aformat_recording.wav> /output <aformat_calibrated.wav> /cal daking.wav

I see. Then you are recording the same source with the gain/trim in the same relative position. And the software can tell you how much to adjust up or down to get them all the same. (This adjusts for the small differences between inputs).