Low Noise Sound card
Arny Krueger wrote:
"Ian Bell" wrote in message
0dB has no meaning.
Actually, it does. In the digital domain 0 dB is commonly equated with FS.
No, that is 0dBFS.
While the units are arbitrary and may be confusing to people who still think
100% analog, it is both meaningful and commonly used.
No it is not.
Input termination in both cases is unspecified.
If the input is a mic input, then the usual standard of 300 ohms applies.
It is a power amp, it does not have a mic input. 300 ohms is NOT the
'usual standard for a mic input'
If the input is a line level input, then the source impedance is usually
such that system performance is not affected that much by probable
variations.
You miss the point. How is the input terminated when noise is measured -
obviously it is not left open circuit is it?
Output termination is unspecified.
The noise performance of line level outputs is minimally affected by
probable and reasonable variations in load impedance.
No bandwidth is specified.
Relevant and already mentioned
No weighting or not is specified.
Relevant and already mentioned
No mention of whether the measurements are rms, peak, quasi-peak
Both SNR and DR are ratios of two measurements. It is most important that
both measurements be done under the same circumstances.
In fact they generally are not since a signal and noise have quite
different characteristics. The signal will be measured rms. The noise
can be measured in several ways each giving a different figure.
Variations in the way the above are specified can make a
large difference to the 'measured' value
Some yes, some no.
and I bet you
can guess which set the marketing department will want to choose.
One other benefit of the solid state/digital revolution is that SNR and DR
performance is often so good ( 100 dB) that most variations in how they are
mentioned don't matter that much.
Rubbish. Once again, SNR and DR are different animals. Achieving a 100dB
DR is not hard but unless you run your amp close to clipping all the
time you will not achieve that as a SNR.
The marketing guys are as active as ever in trying to make their product
appear superior to its competitors and will choose the measurement
methods that best do that.
Cheers
ian
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