"GaryMedia" wrote in message
...

Going back to THD+N as a suspect, I took the time to translate the
traditional percentage specification into dB in order to get a better
feel for what numbers the relationships are.

Behringer MX3242X THD+N = 0.005% = -86dB
Alesis Studio 24 and 32 THD+N = 0.001% = -100dB

Checking through some of my other equipment and looking around on the
web *almost* convinced me that I was on to something in that the
Focusrite, dbx, MOTU 1224 all had this spec in the -100 dB or better
ranges ...even the Studio Projects VTB-1 was at -97dB.

The theory took a torpedo in the side when I looked at the Avalon
preamps. The AD2022 had a spec of 0.05% for distortion which is -66dB.

Either that figure is a typo, or just more evidence that clearly
something else is going on here in the world of audio.

The latter, I'd say. THD, or THD+N, is essentially a meaningless number
without (a) information on the conditions under which it's being measured
(level, load impedance, settings, etc.); (b) information on what frequencies
are being measured; and, most important, (c) information on the harmonic
spectrum produced. A low level of 7th harmonic distortion is a lot more
audible than higher levels of 2nd.

Backing up for a minute, THD is just one way of mapping the nonlinearities
of an amplifier circuit, and for most modern equipment, not a very good one.
IMD measurements can sometimes be more revealing, but we still haven't found
a way to map these nonlinearities in a way that correlates perfectly with
audibility, except in extremely bad cases (e.g., somethiing that measures
30% THD under normal operating conditions is likely to sound distorted).

Peace,
Paul