[Arny Krueger]

"Ian Bell" wrote in message

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.

Yes, so your use of the word "no" must be some kind of terrible mistake on
your part.

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.

Assertion without support, which should be immediately dismissed.

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'

Good modern power amps are common, and do not have that much variation in
their noise performance with normal variations in source impedance.

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?

I guess you've never measured the actual noise coming out of a good modern
power amp with the normal range of source impedances. They often don't vary
all that much. Remember, this is not legacy vacuum tube equipment which was
generally far noisier.

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.

While people could be stupid and compare a noise level measured in
peak-to-peak volts to a signal measured in average volts, I know of no
actual cases where this happens, except perhaps in your mind, Ian. There
could be equipment noise that has a high crest factor, but nature does not
usually go down that path. What is then left is a few dB of ambiguity, and
most good modern equipment (which is common) is not so noisy that a few dB
is a deal breaker in actual use.

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.

Dismissive, unsupported claim, again itself worthy only of dismissal.

Once again, SNR and DR are different animals.

A truism - therefore something that actually sheds no signficiant light. Why
do you obsess over these things, Ian?

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.

Another truism.

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.

The myth is that some equipment is head-and-shoulders better than its
competition. Everybody pretty much feeds from the same trough.