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Gear / Technical Help => Microphones & Setup => Topic started by: Gutbucket on January 17, 2006, 09:12:00 PM
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Hi all,
I've been lurking, getting ready to jump back in after years away from tapin'. More mundane questions to come from me be sure, but I'm wondering if anyone here has heard of or had any experience with a MPT (Matrixed Pressure Triplet) micing setup? Seems to be a baffled omni array of three capsules arranged at equal 120deg. intervals around a cylinder or sphere. Center capsule points forwards at 0deg or 12 o'clock, left capsule at 120 deg or 8 o'clock, right capsule at 240deg or 4 o'clock. Matrix as follows: Center signal is split evenly L-R, Left signal is split between L and mixed 18db down with phase reversed to the R channel, Right is opposite of Left (routed to R and 18db down with phase inverted to L).
Seems like sort of the bastard love child of a M/S setup and sphere bafflled omnis.
I found a cello recording through Amazon done this way but can't find the link & turned up a couple AES papers but I'm hesitant to drop $20 to download the PDF (latest one) http://www.aes.org/e-lib/browse.cfm?elib=5560 (http://www.aes.org/e-lib/browse.cfm?elib=5560) which seems to describe something like that Holophone egg-shaped 5.1 mic http://www.holophone.com/home.html (http://www.holophone.com/home.html)
I noticed in one of Moke's posts (edit- make that spcyrfc, Moke was explaining building the J-disc) in an old thread on spaced omni's vs. Jecklin disc http://taperssection.com/index.php?topic=800.105 (http://taperssection.com/index.php?topic=800.105) he was building DIY Jecklin discs & mentioned the possibility of a tri-disc setup with three mics that might be used for micing a circle of musicians (Reply #106). Got me thinking again.. and imagining three mini-omni caps in a headband for manipulating a stealth HTRF rig after the fact like a M/S mixdown..
Maybe just a load of %$*, forgive me if I'm overstepping my newmember status, curious for your thoughts though.
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looks like a lot of work.
http://sound.eti.pg.gda.pl/student/tn/MicrophoneTechniques_I.pdf
look on page 45-48.
Ive only seen a few things on it(i was researching Decca tree) and everything i saw indicated that it was sort of thin sounding and unpredictable. I will see if I can dig up the pages.
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this looks like Moke's dream :lol:
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There seems no limit in ways to place mics in relation to some kind of baffle mechanism. Microphone method experiementation has become an enjoyable and fun art-form for amateurs and profitalble for recording professional business for over 50 years.
Question is: IS WHATEVER YOU ARE DOING WITH MIC METHODS CONSISTENTLY WORKING AS INTENDED?
Trouble using the many 'baffle' sphere/disk (THAT ARE NON-HRTF) types is lack of ability to record what can be heard IN A CONSISTENT MANNER. These baffles do their own thing (not our thing) that mostly does not relate to our (human psychoacoustical related) needs for satisfying you-are-there recording methods. As a result, these tend to be 'special effects' mic methods that sometimes work OK, and sometimes not at all.
True person-headworn (or exact HRTF baffled) omni mics seem the most consistent in my experience. See my site page www.sonicstudios.com/tips.htm (http://www.sonicstudios.com/tips.htm) for more links for on this interesting subject.
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No ears on the dummy head, please. I'll use my own.
http://sound.eti.pg.gda.pl/student/tn/MicrophoneTechniques_I.pdf
look on page 45-48.
Ive only seen a few things on it(i was researching Decca tree) and everything i saw indicated that it was sort of thin sounding and unpredictable. I will see if I can dig up the pages.
Thanks Teddy, that link has some good info, though not much on MPT other than line drawings of the layout (I gotta wonder what 'MPT z trzecia wersja obudowy' means) I really liked the virtual mic plots for dematrixed M/S using different capsule patterns for mid with varying gains (p.14), never quite saw it presented that way before.
Time to figure out how to T you!
[edit to test editing way-old posts for Brian S]
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yeah, its polish. To t folks you need 50 posts, at which point you will see some letters under peoples names. gdttoo and ptbm the gdttoo is a + and the ptbm is a - no worries on that end. still looking for those MPT links.
No ears on the dummy head, please. I'll use my own.
http://sound.eti.pg.gda.pl/student/tn/MicrophoneTechniques_I.pdf
look on page 45-48.
Ive only seen a few things on it(i was researching Decca tree) and everything i saw indicated that it was sort of thin sounding and unpredictable. I will see if I can dig up the pages.
Thanks Teddy, that link has some good info, though not much on MPT other than line drawings of the layout (I gotta wonder what 'MPT z trzecia wersja obudowy' means) I really liked the virtual mic plots for dematrixed M/S using different capsule patterns for mid with varying gains (p.14), never quite saw it presented that way before.
Time to figure out how to T you!
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It has sparked some interest in me too... Since I'm an AES member, maybe I'll download the paper (it's only $5).
Yesterday I hired to recorded a 40 piece steel drum band. I still haven't finished my decca tree, so I used my 1 metre bar with QTC-1s/QTC-40s on the bar, plus to omni's in the center. Because of where the bass drums were, I ened up placing some SR77s/SR-30s near them to help pick them up a bit more.
I mixed the recording this morning and while not bad, I need to build my decca tree.
Wayne
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Holy crap . . . the title of this thread, "Matrixed Pressure Triplet baffled omni array?" is enough to make my head spin. Say what?? :P
Welcome to the board, Gutbucket.
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Thanks for the welcome all..
Found a link to a commercial solo cello release using this technique http://www.amazon.com/gp/product/B000001MRN/102-3860986-4629756?v=glance&n=5174 (http://www.amazon.com/gp/product/B000001MRN/102-3860986-4629756?v=glance&n=5174). There are WMA samples on the page, but I can't really tell much with my freebe dell computer speakers. The only review mentions exagerated treble & lack of warmth, but how can you trust a single review on one recording to evaluate the technique? I may order a $10 copy just to check it out.
Also dug up the bit below from my old files, traslated using Google translation from French I believe:
Let us speak finally about another system, not marketed, which can be added with this category of hybrid stereophonic sensors. It is about Matrixed Pressure Triplet (MPT) of the Belgian André Defossez 24. Three omnidirectional capsules are laid out in an equidistant way on surface curved of a cylindrical baffle, with thus a difference of 120° between them. Capsule A points with 0°, the capsule B with 120° on the left and the capsule C with 120° on the right. The signals for speakers are produced by dieing, i.e. preestablished mixing of discrete channels, in a console. Capsule A feeds the left and right channel jointly, the capsule B feeds the left channel and, with an attenuation of 18 dB and an inversion of polarity, the right channel. One makes in the same way for the capsule C which will feed the right channel directly and, with the attenuation of 18 dB and the inversion of polarity, the left channel. Wanting to dissociate itself what was done until now, the inventor of the MPT places his invention in a crenel up to that point remained free: stereo sensor not coincide with dieing. It is indeed true. If the dieing of a sensor not coincide can appear bold, let us recall that the baffle ensures a sufficient attenuation of the high frequencies and control thus filtering out of comb. The MPT surely answers a certain number of criteria of the model of association of Theile, but we must believe that the respect of the model would be surely more complete if the baffle were of spherical form rather than cylindrical. The cylinder, while setting an acoustic obstacle passably different from the sphere or head, can make spectral modifications being able to be wrongfully interpreted at the time of the reproduction. This known as, space information is encodée on two axes, X and Y, and the MPT could thus be regarded as a two-dimensional sensor.
Sounds like this guy is arguing that the directional effect the baffle has on the omni cap's high frequency response eliminates or reduces comb filtering problems that would be expected when matrixing ('dieing') non-coincident, closely spaced capsules.
Trying to guage if it's worth rigging up a little sphere baffle experiment, but I don't have three matching omnis. Maybe I'll throw this one over to that Yahoo DYI discussion group I've heard about that plays around with the cheap Panasonlic caps. I've seen some pics of some bizare looking DYI M/S & Blumlien configs made from those little 1/4" (cardiod) electrets.
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I bought the AES paper and there are diagrams for building the rig he used for the paper. Since I have two matched pairs of Earthworks QTC1/QTC40, I could try this, but I want to read the AES paper in more depth before I do much. There are some samples of the audio waveforms using this method, which were run in a test environment. I need to understand these a bit more because at first glance, they don't look impressive.
Wayne