Large Diaphragm condenser for choirs/orch/etc.

Posted: Sun Jan 27, 2008 7:30 pm

Cucco wrote:

Since this delta always results in a figure of less than 94dB, is it not safe to assume that NO mic is suitable for 24bit recording?

If you were to find music (and acoustical surroundings) that could actually provide a dynamic range beyond 100 dB, the microphones' self noise might become a limiting factor... But this very unlikely to happen, isn't it? Very Happy

Also consider that practically all 24-bit converters in the market have an SNR that does not even reach the theoretical SNR for 20 bit (120 dB)...

24-bit recording will help keep converter noise away when recording levels are set too carefully, e.g. with peaks at -20 dBFS or less.

And while a noisy mic's self noise (e.g. 26 dB) might become noticeable in quiet surroundings (the DPA 4090 being a case in point, totally useless as e.g. AB main mic), a quieter mic's self noise of 6-15 dB is likely to be inaudible.

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My point is, determining SNR is a good factor for demonstrating a mic's self noise, but little else of relevance since it would be more accurate to measure the output of the microphone with a specified input

That's what sensitivity measures (mV/Pa).

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and its output with no input.

That's the self noise...

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Since the self noise output does not vary based on input yet output signal does, how does the existing SNR have any relevance to actual performance of the mic?

SNR and self noise are directly related, and both will tell you whether a mic is noisy or not. In relative or absolute terms...

Mind that SNR (as in the above examples) is a standardized measurement, allowing direct comparison between different microphones. A mic's SNR is not equal to its dynamic range. The latter will take into account a mic's max SPL handling. (Max. SPL - Self noise = dynamic range). This figure does not allow direct comparison, since some mics handle greater SPL than others. Hence the SNR figure, based on a fixed SPL value.

Cucco wrote:

Take 2 mics. One of which has a 7 dB self noise and a low sensitivity (11dB/PA).The second has a high sensitivity (40dB/PA) and a 20 dB self noise. To get the same level of signal out of the first mic, you'd have to amplify it by let's say 13dB (I haven't done the math so I'm probably way off - let's just work on hypothetical.)

The problem with the math here is that sensitivity is measured in mV/Pa, not dB/Pa.

Daniel

Posted: Sun Jan 27, 2008 9:57 pm

My bad - I mistyped "db/Pa" vs. "mv/Pa"

All else that's stated is stuff that I'm aware of and do not dispute. (Actually, where you quote me as stating "and its output with no input." is equal to self-noise - I had made that statement in the previous paragraph, so we're on the same wavelength.)

David's information is helpful. Given his examples, I'd like to do some testing of my own to validate what's been said.

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