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amplification of mic self-noise

Subject: amplification of mic self-noise
From: "jessehammons" <>
Date: Wed, 03 Mar 2004 17:25:37 -0000
Out of curiousity, if a microphone has 5 dB of self-noise, and you
turn the gain on the pre-amp up to 50 dB, how loud is resulting signal
(assuming the microphone is place in a sound-proof chamber of some kind).

What if the mic has 10 dB of self noise?

I'm trying to understand how quiet a place can be before one has to
give up and use some sort of parabolic dish to collect more sound.
Even the very expensive microphones talked about on this list have a
self-noise rating of 5-6 dB or so.  A quality pre-amp won't introduce
much extra noise on top of that, but I am assuming it will amplify the
mic noise just as it would any other signal.

I used my new "pro" recording setup (rode NT1-A mics + mic2496
pre-amp...It's "pro" for me anyway) to record a location the other
night with the gain turned up to around 50 dB or so.  I haven't fully
analyzed the test recordings yet, but I think I can hear the mic
self-noise in the recording using that amount of gain on the preamp.
I'm wondering if I can calculate whether that is possible or whether
the self-noise value wouldn't even be audible if all my equipment is
running within spec.

Thanks,
-Jesse





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