> With any mic you can find self-noise given S/N
> 94dB - S/N =3D Self-Noise
> so 34dB in this case.
Paul,
I won't quibble about your arithmetic as a signal to noise ratio is
meaningless for a microphone anyway. :-)
A dynamic range of 60 dB is rather poor as that's what we experience
every day. A good telephone can do that. It depends what weightings
are put on the sensitivity and noise measurements. Manufacturers are
keen to publish the best figures, but these may not correspond to what
we hear, especially if we are recording birds. You can't filter out
hiss at bird frequencies without losing birds.
The fundamental noise figure is the equivalent noise relative to the
noise of air molecules, (Johnson noise) but this itself rises with
frequency. Sennheiser quotes two noise figures, for instance for the
ME-66: Equivalent noise level =3D 10dB and Equivalent noise level
weighted as per CCIR 468-3 =3D 21dB.
http://en.wikipedia.org/wiki/ITU-R_468_noise_weighting
This weighting peaks in the higher kilohertz and falls steeply after
10KHz and corresponds with how we perceive hiss. That's where the
extra 11 dBs come from but you can't compare that with figures from a
cheapo mic. You won't easily find noise figures lower than these
anywhere. Even the much more expensive MKH-416 is a couple of dBs
noisier.
Most manufacturers will quote the lowest noise figures they can get
awasy with. In many cases you would be wise to add the 11dB as above.
Even then you won't get the best noise ratio unless the mic feeds into
a maching impedance input.
The practical noise test is to record in the quietest environment you
use with and without a muffling cover like a padded jacket. Listening
back will tell you if microphone and input noise is a problem.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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