Eugene E Dorcas wrote:
>Can you calculate the output noise from other specs such as
>signal-to-noise ration and sensitivity??
>
>For instance: If the sensitivity is -32dB and the SNR is 75 dB,
>what would the output noise be??
Mic signal-to-noise is measured from 1 Pascal, which is 94dB SPL.
If the SNR is 75dB, you can calculate the self noise of the mic:
94-75 = 19dB SPL (probably the SNR was spec'd in dBA, if so it would
be 19 dBA).
The sensitivity is more relevant to the question of whether that mic
would get its own noise above a particular preamp's input noise
level, called Equivalent Input Noise (EIN). If it does by more than a
few dB, then you can get the best performance from the mic.
http://www.rane.com/note145.html
The noise output of a mic with 75dB S/N and -32dB sensitivity (very
hot!) would be -(75+32) = -107dBV. dBV because the sensitivity is
measured re 1 Volt (1Pa/1V).
0dBu is 2.2dB below 1V (don't ask), so the noise output voltage of
the mic in Haleakala crater would be -104.8dBu. That would be way
above the noise of even a commonplace preamp (like EIN = -125dBu). A
mic with 10dB lower output than yours, like the Shure WL183, is still
hot enough to make the noise of a cheap preamp irrelevant.
Another confounding factor would be that preamp EINs used to be
measured in dBm, and some still use that measure. Let's not go there,
either. Any real audio engineers here, please check my figures.
-Dan Dugan
(I'm not an engineer, but I play one at work.)
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