> Actually, not. Quiet forest or desert ambiences show up the
> self-noise of mics mercilessly. That's why Rob Danielson made a
> specification of 16dBA or lower for mics suitable for quiet
> ambiences.
Dan,
That must have been A-weighted. CCIR 468-3 gives about a 11dB higher
figure but it is a peak measurement not RMS. This noise measurement
covers hiss, which is the noise that worries us. The 468 curve
http://en.wikipedia.org/wiki/ITU-R_468_noise_weighting
shows the difference from the A-curve. Note the noise figure is
actually excess noise over basic thermal noise. A mic "signal to noise
ratio" is just about meaningless as we are looking at a noise to
signal ratio.
Where we gain with internally powered mics is in swamping the mixer or
recorder input noise. We blame the mic but it's doing its best. I
think I would aim for a 468 weighted noise figure of 26dB or lower.
There is a solution to hiss. Filter out everything below 10kHz and if
there aren't nature noises up there, filter it out.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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