Jesse,
I only know this from school, so I might be wrong. But I think this
is how you should process the numbers.
If your mic has 5 dB self-noise, and the preamp has 50 dB gain, then
both the self-noise and the signal from the mic are 50 dB louder.
Assuming the input signal is 20 dB then; output of preamp is 5 + 50
=3D 55 dB noise and 20 + 50 =3D 70 dB signal.
The signal to noise ratio at the mic input is 20 - 5 =3D 15 dB.
At the preamp output it is 70 - 55 =3D 15 dB at best; if the amp has
added sef-noise too, the SNratio of the preamp output might be worse
then the SNratio of the mic.
The only thing an amp does is making signals stronger, both the
wanted audio signal and the unwanted self-noise.
The variables we have are:
- self-noise of the mic, and the preamp; these should be low values
- gain of the pre-amp; this one doesn't matter
- signal to noise ratio of the pre-amp; this one is best a high value
- signal strength of the source; this one is best a high value
Regards, Evert
--- In "jessehammons"
<> wrote:
>
> 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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