Steve, you wrote:
> So here's the question --- what microphones are people using with the
> fancy machines that digitize at 96 and 192 KHz?
In my opinion, normal audio recording at 96 or even 192 kHz does not
make much sense. It's just some kind of an esoteric or "homeopathic"
approach, which might work if one believes in it ;-). As far as I
know, there is still no proof that we can hear anything above 20 kHz.
The only argument that I would accept is that the anti-aliasing
filters in the 96 or 192 kHz sampling mode do not need to be very
sharp. A more relaxed (or a higher frequency cutoff) filter will
introduce less ringing and phase distortions at the upper frequency
limit of our hearing range.
> I understand that there are several (very expensive) measurement
> microphones that cover the larger frequency range but the ones I've
> seen, together with things like the Earthworks microphones, have a
> fairly high noise level. (22 - 28 dB A or higher).
Yes, it seems to be impossible to design a microphone that provides
both a low inherent noise floor and a large bandwidth from 50 Hz up to
50 kHz and beyond.
> When I visit web pages of manufacturers and view spec's for all the
> usual devices people talk about here --- none of them say how the
> microphones work in the 25+KHz range.
I know of two microphones that try to adapt the 96/192 recording mode:
Sennheiser MKH800 and Schoeps MK 21H + CMC 6:
http://www.schoeps.de/E-2004/specs-mk-ccm21h.html
Both models achieve the extended frequency range simply by boosting
the higher frequencies. However, due to physical constraints, the
noise floor at the very high frequencies above about 30...40 kHz will
also be increased. Therefore, the manufacturers do not specify the
poor noise figures at those high frequencies...
If you are interested in recording ultrasounds for more scientific
purposes (e.g. for bats, rodents or bush crickets), then you should
have a look at microphones or bat detectors that have been optimized
for that purpose. Avisoft Bioacoustics for instance offers two solutions:
a) Phantom-powered ultrasound microphones for common 96/192 kHz recorders:
http://www.avisoft.com/usg/microphonesP48.htm
b) Dedicated laptop (or UMPC [=3D ultra mobile PC]) based recording system:
http://www.avisoft.com/usg/usg116-200.htm
Regards,
Raimund
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