Re: Is this a good way to test pre-amp hiss of a digital recorder?


Pooh Bear wrote:


You won't see quite as much as 6dB because of the preamp's self noise. The better the
preamp, the bigger the difference you'll see. Noise sums as the sqrt of the sum of the
squares.

Ignoring smaller than unit values of dB, I did in fact see about 6 dB
difference.

To measure the preamp's noise*voltage* you can indeed short the input but this won't
establish the input noise *current* which will add to the figure when the preamp sees > a real mic.

I follow that, this is getting too theoretical for a practical test. A
real mic has varying amounts of noise output depending on its design.
In additon, it's very difficult to acoustically isolate a mic, so you
can't get rid of any acoustic noise that gets converted to output
voltage (seen as noise at the preamp output) because of what a
microphone is suposed to do. So testing with a real mic is out the
window, and emulating a "standard" mic with a resistor probably doesn't
really emulate any real microphone. It's a way to standardize the test
procedure, however - if (and only if) everyone used the same procedure,
and the same resistor.

.

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