On 2007-10-02, Iain Churches wrote:
"Arny Krueger" wrote in message
. ..
"John Phillips" wrote
in message

I have sometimes pondered (without real cause, I admit)
about whether the "usual" IMD tests are good enough as a
predictor of audible IMD effects.

Not really.

Agreed. They must be better than nothing, but probably have
little bearing on what might be happening in a complex musical
signal.

That's what has always concerned me. I no longer design and build kit
(for 20 or more years and it was only ever a hobby). Although I got
to understand linear distortions and noise in audio systems I never did
get to grips with understanding non-linear distortion. Of course I
did understand the basics but I always felt the simple IMD tests were
not the complete way to evaluate system non-linearities. However I'm
not really sure.

Do you think the normal two-tone IMD tests (from SMPTE,
DIN, IEC, etc.) provide an adequate basis for testing something
where (I postulate) more complex IMDs may be the more
audible effect?

Not really.

There seem to be several opinions regarding the
frequencies of the fundamentals used in such tests.
Is there any standard?
I have seen 70Hz and 6kHz mentioned, and
also 19kHz and 20kHz.

See, for example, http://www.rane.com/par-i.html (look down for IM/IMD)
for some of the standard IMD test methods.

--
John Phillips