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Author Topic: miniDSP AmbiMIK-1 Ambisonic Mic  (Read 2650 times)

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Offline Len Moskowitz (Core Sound)

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #15 on: July 14, 2020, 11:15:40 AM »
"Generically calibrated" is the opposite of "individually calibrated."

Ambisonic microphones work on principles that depend on the very small differences between their capsules, plus a bunch of other factors. In this case and for the Zoom H3-VR, just because a microphone has four capsules mounted on a tetrahedral mount, that doesn't mean that it will work well.

It turns out that every microphone capsule is different. They might all meet the manufacturer's specifications, but those specifications have ranges of variation, and those variations are incredibly important for ambisonic microphones.

There are also other sources for variations in addition to the capsules.

Calibration is the process that measures the variations and provides corrections for them.

Because it takes time and equipment and manpower to test each of the capsules and then match them into sets, and because it costs money to test each assembled ambisonic microphone to develop correction files for each complete microphone, the manufacturers compromise. They make the assumption that all of their capsules are sufficiently matched, and all of their assembled microphones are sufficiently identical to use a single generic calibration correction.

From the beginning the assumptions are wrong. And as the microphones age, the assumptions get even worse. You're still stuck with the original generic calibration.

That's why each ambisonic microphone needs to be individually calibrated, and supplied with its own correction file. And as it ages, it will need to be re-calibrated.

Ideally, each set of capsules should be matched for a bunch of specifications - not just frequency response and/or sensitivity. And then when they're assembled into the microphone mount, each microphone should be measured so that its performance can be corrected with an individual calibration file.

All Core Sound OctoMics and TetraMics are individually calibrated. We recommend re-calibration every two to three years, depending on application. We offer a recalibration service for our microphones.

(We also offer an initial calibration service for other manufacturers' ambisonic microphones, including those from Rode, Sennheiser and the old Soundfield.)



« Last Edit: July 14, 2020, 12:46:03 PM by Len Moskowitz (Core Sound) »
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Offline MIQ

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #16 on: July 14, 2020, 12:34:58 PM »
Hi Len,

I appreciate you taking the time to explain that.  When they state that they worked to create a "VST plugin specifically calibrated for the ambiMIK-1 with over 1200 measurements", they are talking about taking measurements of the mics in development and applying those measurements/calibrations to all the mics they produce, regardless of the slight differences in the individual capsules actually being assembled. 

I've read a fair bit about mic calibration, even the old Soundfield design (I'm a big fan of Gerzon), and can see how the costs could quickly get out of hand for a budget minded product.  As usual, the more accurate you get, the more time and money it takes. 

Offline Len Moskowitz (Core Sound)

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #17 on: July 14, 2020, 12:39:57 PM »
When they state that they worked to create a "VST plugin specifically calibrated for the ambiMIK-1 with over 1200 measurements", they are talking about taking measurements of the mics in development and applying those measurements/calibrations to all the mics they produce, regardless of the slight differences in the individual capsules actually being assembled. 

Yes. And the variations in mounting the capsules in the capsule mount. And the effects of the cables behind the capsules on the venting of the capsules. And others.

Some of the "slight differences in the individual capsules" are not slight. Some are quite large and significant.
« Last Edit: July 14, 2020, 12:45:18 PM by Len Moskowitz (Core Sound) »
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Offline heathen

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #18 on: July 14, 2020, 12:50:56 PM »
Len, how do you know for certain whether or to what extent other manufacturers calibrate the capsules for their ambisonic mics?  Or what those manufactures' internal specs are for the capsules they use in their ambisonic mics?
Mics: AT4050ST | AT4031 | AT853 (C/SC) | Line Audio CM3 | Sennheiser e614 | Sennheiser MKE2 | DPA 4061 | CA-14 omni Pres: CA9200 | DPA d:vice Decks: Zoom F8 | Roland R-05

Offline Len Moskowitz (Core Sound)

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #19 on: July 14, 2020, 01:05:18 PM »
Len, how do you know for certain whether or to what extent other manufacturers calibrate the capsules for their ambisonic mics?  Or what those manufactures' internal specs are for the capsules they use in their ambisonic mics?

We buy their mics and test them. As they do for ours.

We know that all the manufacturers match their capsules. Some do a better job than others. Some clearly don't test other important specifications. None of them calibrate completely assembled microphones, except perhaps one, and we think that they don't do a very good job. Almost all use a generic calibration.

In one case a generic calibration is warranted because they use MEMS elements as capsules; they are reliably long-term stable. They're noisy though.

The rest of the manufacturers use standard electret capsules. No matter how tightly matched they are during manufacture, two years (or less) downstream they've drifted.

One microphone manufacturer provides individual calibrations that correct for sensitivity variations only. They buy their capsules (they don't manufacture them) and presumably decided that correcting errors is less expensive than sorting for tightly matched capsules. They don't provide individual calibrations for the assembled microphones.

If you really want to know how good an ambisonic microphone is, look at its decoded polar directivity patterns - for example on a tetrahedral first-order microphone, look at the B-format's omni and the figure-8 channels . If they don't publish them, ask them why.

If they publish a frequency response specification, does it provide tolerances? If not, it's not real - it's a marketing specification. (Individual calibration allows for roughly two more octaves of bass.)

« Last Edit: July 14, 2020, 07:38:47 PM by Len Moskowitz (Core Sound) »
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Offline fotoralf.be

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #20 on: August 23, 2020, 03:33:34 PM »
disappointment.... "oh dear, it is a USB mic"

Is there something generally wrong with USB mics?

@all others:

Couldn't we simply agree that it isn't as good as microphones made by Core Sound, because obviously nothing could ever be, and carry on with discussing the AmbiMIK-1?

Not everybody needs a Ferrari to drive to work. Not even everybody wo could afford one, let alone the rest of us.

Ralf
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Offline MIQ

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #21 on: August 23, 2020, 10:53:02 PM »
Ralph I don't think there is anything "wrong" with USB mics.  I imagine most of the tapers here are not interested in using them because the makers of these mics usually make compromises in performance that tapers are not interested in living with.  Max SPL, polar response, self noise are compromised in many of these mics to reach a price point.  They are not aspirational mics that most people dream of owning someday.  With that said, I think they will continue to get better and the cost/performance trade-offs will not be so severe.  Len's mics cost more because he is striving for better performance at a slightly higher price point.  I wouldn't say Len's mics are at Ferrari price points.  It still costs a certain amount of money to make a quality product at low volume. 

The Senn Ambeo is $1300  https://www.sweetwater.com/store/detail/AMBEO--sennheiser-ambeo-vr-microphone?mrkgadid=3341927511&mrkgcl=28&mrkgen=gpla&mrkgbflag=0&mrkgcat=studio&recording=&acctid=21700000001645388&dskeywordid=92700046934908799&lid=92700046934908799&ds_s_kwgid=58700005285215127&ds_s_inventory_feed_id=97700000007215323&dsproductgroupid=744089619784&product_id=AMBEO&prodctry=US&prodlang=en&channel=online&storeid=&device=c&network=g&matchtype=&locationid=9030049&creative=353564234315&targetid=aud-374460618936%3Apla-744089619784&campaignid=2005216453&gclid=Cj0KCQjwp4j6BRCRARIsAGq4yMGHS2fgU0PoxqvxdcWzFwUZk5Z7rxDrfNSyOXYmGMyRIFDt1FbBgaYaAj-vEALw_wcB&gclsrc=aw.ds


The Rode NT-SF1 is $1000
https://www.americanmusical.com/rode-nt-sf1-soundfield-true-condenser-ambisonic-mic-kit/p/ROD-NTSF1?src=Y0802G00SRCHCAPN&adpos=&scid=scplpROD+NTSF1&sc_intid=ROD+NTSF1&gclid=Cj0KCQjwp4j6BRCRARIsAGq4yMHhSpNHZ7EvDorOYe2-uGTa46pgUu_fM_VIkgu9r15_fObgO4yE-dAaAqAjEALw_wcB

The Core Sound Tetra is $825
https://www.core-sound.com/TetraMic/12.php

The mini DSP mic is $325
https://www.minidsp.com/products/acoustic-measurement/ambimik-1

Seems like there's room for a few manufacturers at different price points.  Get what you can afford and start using it.  Just don't expect them to all have the same performance.  Is there something else you want to know about the miniDSP?  I think it looks cool for an affordable ambi mic.  I also really like the DIRAC guys from working with them in the past, so I posted it here.  I bet it works well, but I've never played with one.  If no one wants to buy it yet, not even me, I guess we don't have much to say.
« Last Edit: August 24, 2020, 02:28:28 AM by MIQ »

Offline fotoralf.be

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #22 on: August 24, 2020, 06:07:44 AM »
I don't see why a microphone with a digital output is necessarily of inferior quality. BOM wise, there shouldn't be much difference between four good quality analog output stages and a decent ADC with four channels. Incorporating the necessary correction for an ambisonic array in a digital output configuration should be easier and more predictable than having the signal go through the user's analog preamps and ADCs of unknown make, specs and quality and then doing the correction in the computer after goddess knows what's happened on the way there.

Yes, most USB microphones currently on the market are low-end products but there is no rule saying they need to be. Certainly not from the technical side.

Having said this, I think there should be a future digital interface other than USB allowing a synchronised connection of several digital microphones without timing problems. Not so much a problem with an ambisonic mic that will mostly be used on its own.

BTW the price here in Europe is around 650 USD. The usual margin of 3 percent our importers scrape their meagre living from...

Ralf
« Last Edit: August 24, 2020, 10:05:37 AM by fotoralf.be »
Photography and industrial audioscapes from Western Europe. - Sound examples: http://aporee.org/maps/projects/fotoralf - Blog (German): http://the-real-fotoralf.blogspot.com

Offline DSatz

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #23 on: August 24, 2020, 01:11:02 PM »
Until/unless I become aware of a reason to think otherwise, basically I consider USB mikes to be fine for podcasting, on-line meetings and casual tracking, but nothing more. I'm probably biased from the early days of USB (1.0 and 1.1), but I simply don't trust a USB connection to handle (say) 24-bit two-channel audio at 48 kHz without ever dropping any samples. To the best of my knowledge, the basic scheme of the interface has no provision for guaranteeing any particular, required level of availability, bandwidth and buffering to a given peripheral.

I assume that newer versions with higher maximum data rates are "better" in that one has better luck with them in general--but I simply don't know for a fact that my signals will get through to the computer (or whatever) unchanged, so I don't consider USB a suitable type of interface for serious recording.

Again, subject to my finding out that things have changed fundamentally ...

« Last Edit: August 24, 2020, 01:12:53 PM by DSatz »
music > microphones > a recorder of some sort

Offline fotoralf.be

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #24 on: August 24, 2020, 01:30:54 PM »
...but I simply don't trust a USB connection to handle (say) 24-bit two-channel audio at 48 kHz without ever dropping any samples.

You mean all those USB computer audio interfaces delivering multiple channels at 48 kHz/24 bit  and some even at higher rates all don't work correctly? Or is this a special phenomenon that only occurs with USB microphones?

What kind of digital connection would you recommend for transferring the digitised audio from analog microphones into a computer?

Ralf 
Photography and industrial audioscapes from Western Europe. - Sound examples: http://aporee.org/maps/projects/fotoralf - Blog (German): http://the-real-fotoralf.blogspot.com

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #25 on: August 24, 2020, 08:46:15 PM »
DSatz,

I am with you for USB microphones, which are often inexpensive and have who-knows-what for ADCs in there.  The majority of them still max out at 16/48, though there are a few that do better nowadays.

As far as USB being a reliable interface for recording, I think the newer spec versions of USB are totally reliable.  The new MOTU M2 interface I currently use uses USB 3.1 type C, and it has been nothing but rock-solid for me.  As long as you are on at least USB 2.0, you have plenty of room for multichannel, high-bitrate recording.  Look at some of the video reviews from Julian Krause for some good technical analyses of these newer interfaces.

There are many high-quality USB interfaces out there that are using the newer specs.  If the 10 gb/s of USB 3.1 gen2 isn't enough for you, there is Thunderbolt 3, which will do 40 gb/s but your selection will become smaller.

There's MADI and Dante, but those are really overkill unless you have very high track counts or need to go long distances.
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Offline EmRR

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #26 on: August 24, 2020, 09:33:27 PM »
There's not a locking USB connector, is there? 
Mics: DPA 4060 w/MPS 6030 PSU/DAD6001/DAD4099, Neumann KM 131, KMR 81i, Oktava MK 012, Sennheiser MKH 105, MKH 20, MKH 30, MKH 40, MKH 800 TWIN, lots of other studio appropriate choices
Recorders: Zoom F8n, Sony MZ-R50, portable MOTU based multitrack DAW for client work

Offline heathen

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #27 on: August 24, 2020, 10:37:33 PM »
Until/unless I become aware of a reason to think otherwise, basically I consider USB mikes to be fine for podcasting, on-line meetings and casual tracking, but nothing more. I'm probably biased from the early days of USB (1.0 and 1.1), but I simply don't trust a USB connection to handle (say) 24-bit two-channel audio at 48 kHz without ever dropping any samples. To the best of my knowledge, the basic scheme of the interface has no provision for guaranteeing any particular, required level of availability, bandwidth and buffering to a given peripheral.

I assume that newer versions with higher maximum data rates are "better" in that one has better luck with them in general--but I simply don't know for a fact that my signals will get through to the computer (or whatever) unchanged, so I don't consider USB a suitable type of interface for serious recording.

Again, subject to my finding out that things have changed fundamentally ...

I'm pretty sure even the old USB standards are capable of bit perfect audio.  Check this out: https://thewelltemperedcomputer.com/Intro/SQ/USB_SPDIF.htm
Mics: AT4050ST | AT4031 | AT853 (C/SC) | Line Audio CM3 | Sennheiser e614 | Sennheiser MKE2 | DPA 4061 | CA-14 omni Pres: CA9200 | DPA d:vice Decks: Zoom F8 | Roland R-05

Offline fotoralf.be

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #28 on: August 25, 2020, 04:04:38 AM »
There's not a locking USB connector, is there?

Not on this microphone from the look of it but Neutrik make several versions:

https://www.neutrik.com/en/search?q=usb

Ralf
Photography and industrial audioscapes from Western Europe. - Sound examples: http://aporee.org/maps/projects/fotoralf - Blog (German): http://the-real-fotoralf.blogspot.com

Online WiFiJeff

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Re: miniDSP AmbiMIK-1 Ambisonic Mic
« Reply #29 on: August 25, 2020, 11:21:16 AM »
I was playing around with the Zylia ZM-1 for about a year prior to the Covid lockdown.  This is a 3rd order ambisonic mic using MEMS capsules, 19 channels at 24 bit/48 kHz, over USB to a pocket computer (or more recently a dedicated ZR-1 recorder).  Most of the mixing I was doing was only first order, comparing it to my Josephson C700S which is basically a native B format first order mic without the Z channel (as long as the orchestra isn't throwing violins over your head this is fine, for me).  I did use Reaper with the Zylia Studio Pro plugin to produce "virtual" directional mics, a very neat trick. The next generation of MEMS mics may make this a killer app, for now the C700S is the serious mic.  But the ability of USB to handle 19 channels of 24/48 has not been an issue that I have found.

Jeff

 

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