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anonymous 29 January 2008

Hi everyone,

I'd like a bit of advice about choosing the best gear to get some high quality voice recordings. These recordings will be used for speech recognition research, and what we'd like to do is to have simultaneous, perfectly synchronized recordings of the same person with
*a close-talking mic
*an in-ear bone mic
*an array of 4 closely spaced mics on the chest of the speaker
The whole setup must be battery-powered and portable enough to walk around with.
Ideally all channels will be recorded on one device to avoid synchronization issues but we'd consider 2 separate devices and do some post-processing for synching the audio streams

My questions are:
1) Can you recommend compact mics that can be mounted (4 of them) on the chest (worn on a necklace-type setup)?
2) Do I need to use a recording device with built-in mic preamps? If not, how can I power the mics (most of the ones I've read about requre power)
3) Any recommendations for compact hardware to record perfectly synchronized audio? The budget is around $1000 including mics. So far the best option we've found is to get an M-audio Microtrack II ( http://www.amazon.com/dp/B000VXKPZ6/?tag=r06fa-20 201660559&sr=1-1) for the bone mic and headworn mic, and Zoom H2 ( http://www.amazon.com/dp/B000VBH2IG/?tag=r06fa-20 59&sr=1-2) for the 4-mic array.
4) With the Zoom H2 (records 4 simultaneous channels from its internal mics), would it be feasible to hack off its 4 internal microphones, and solder in the wires from 4 lapel mics with appropriate directionality and positioning?

I know this is a complex problem with lots of options, and I'm sure I'll have more questions based on your suggestions. Any help will be appreciated.

Thanks!

-Alex

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Comments

Boswell Wed, 01/30/2008 - 03:11

I'm sorry to say you are mistaken if you think that the MicroTrack II and the Zoom H2 record more than two separate channels simultaneously. The H2 indeed has 4 internal microphones, but the outputs of those mics are mixed in different ways to give a stereo signal which is what is recorded.

I don't know of an 8-track portable recorder. Some years ago I put one together for some field research work, but it came down to how to house and power an 8-channel digitizing preamp and a laptop all crammed into a backpack and running off a caravan battery.

Cucco Wed, 01/30/2008 - 06:16

Boswell's right. The only 8 channel HD recorders that are portable are WAY outside of your range. (WAAAAAYYYYY - like $25K and up).

As for body-worn mics, you're going to be hard pressed to find 4 of these plus your other mic requirements as well as the recorder for under $1k.

I did a lot of work on speech recognition software and hardware when working for the DoD Biometrics Management Office. We found that the quality of the mic did matter but only as much as False Reject Rates, not as much with False Accept Rates.

Boswell Wed, 01/30/2008 - 07:21

Actually, a pair of those new Edirol R-4s look as though they might do the job. From the blurb, it seems you can sync two of them together to get 8 channels. Although the start point may not be in sync between the two units, they will stay sample-locked, so any time slip between the two groups of four channels could be corrected in post-processing.

anonymous Wed, 01/30/2008 - 19:28

Hi all, thanks for the comments.
Boswell - the H2 manual says that it records the 4 mics into two separate stereo files simultaneously, which implies no mixing. I might have to get one and hack it apart. Anyone know of suitable subsitute mics? I suppose I can measure the DC voltage supplied to the mic leads by the device and try to find other mics that work with that voltage, or perhaps just get long wires and place the original mics externally... Specific recommendations for inexpensive mics would be nice.

mark_van_j - thanks for the R44 suggestion, that looks like a good option, I hope they announce the price and start selling those soon because we need to buy 10 of these setups within a month.

cucco - we would actually like to use inexpensive mics since they do give adequate performance on ASR. The thing i'm not sure about is what kind of mics (condenser? other? powered?) will work with the recorders we're considering (the hacked H2 or something with power like the R44).

Boswell - Thanks for pointing out that the Rolands can sync. I think we'll be ok if the two head mounted mics aren't perfectly in sync with the 4 mic array.

My most important remaining uncertainty is basically about different mic types; Do all mics need power? Do all mics need a mic preamp? Can I consider a multitrack recorder that has 4 or 8 inputs but no mic preamps? I believe there are some products out there like that.

Thanks again
Alex

Boswell Thu, 01/31/2008 - 03:37

mosfet9 wrote: Hi all, thanks for the comments.
Boswell - the H2 manual says that it records the 4 mics into two separate stereo files simultaneously, which implies no mixing. I might have to get one and hack it apart. Anyone know of suitable subsitute mics? I suppose I can measure the DC voltage supplied to the mic leads by the device and try to find other mics that work with that voltage, or perhaps just get long wires and place the original mics externally... Specific recommendations for inexpensive mics would be nice.

Yes, you are right. The user manual says 4-channel recording whereas the info sheet I was looking at says stereo recording. I believe the internal mics are electret, so they will have permanently polarized capsules but require a few volts for the FET followers. If you were to get electret external mics, you could probably wire them in place of the internal ones.

mosfet9 wrote: My most important remaining uncertainty is basically about different mic types; Do all mics need power? Do all mics need a mic preamp? Can I consider a multitrack recorder that has 4 or 8 inputs but no mic preamps? I believe there are some products out there like that.

Any recorder that has mic inputs has built-in pre-amps - it's only line-level input devices that do not have pre-amps. Mic inputs with phantom power are not easily usable for electret mics, so take care.

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