[Arny Krueger]

"Ian Bell" wrote in message


Indeed, and most professional equipment operates at +4dBu
and some at +8dBu and then again a lot of commercial
power amps have an input sensitivity of 2V for full
output.

What you've missed is that there is only a few dB between all of these
numbers. The difference between an objectionally noisy system and an
aceeptable system is generally far more than just a few dB, no matter how
you measure things.

Any of these would do, the point is we are not told which.

It's a hair-splitting, misleading point.

I very much doubt the manufacturer says how the input is
terminated when he measures the amp output noise but I
very strongly suspect he short circuits it to give him
the lowest noise figure. Of course you will not achieve
this figure when connected to a real source.

Again, there are only a few dB difference in the noise floor of line-level
products with reasonable variations in source impedance or load.

Output termination is unspecified.

As per manufacturers guidelines


Which are what?

No bandwidth is specified.

We are talking "audio" so perhaps we can suggest it just
might be somewhere between 20Hz and 20,000Hz?

Yes, but when measuring noise it is very important. Often
a 15KHz bandwidth with well defined slopes is used
because it gives a total equivalent noise bandwidth of
20KHz which is not the same as a flat response from 20Hz
to 20KHz but is does give a better figure.

Again, there are only a few dB difference in the noise floor of line-level
products with reasonable variations in measurement bandwidth.

Many of these issues are bigger issues for legacy vacuum tube equipment,
where the noise levels were generally closer to the edge of perception.