Compensating multi-stage feedback (was: RE: all tranny vca+ )

[Don Tillman]

   Date: Sun, 02 Jul 2000 02:49:51 +0200
   From: Magnus Danielson <cfmd at swipnet.se>

   Would you _please_ elaborate on how 0.001% is more awful than 5%.
   I'd really like to know. Where's the evidence?

Distortion can take many forms; heck, any form.  Some of it might not
show up in standardized measurements, some might only show up as
intermodulation distortion on more complex waves, some of it might
show up at certain levels or on certain types of waveforms.  Harry
pointed out crossover distortion; that's a *great* example.

Product examples, perhaps?  My personal experience is with the old
Peavy mixers and the mixer section of the Yamaha MT2X 4-track cassette
deck.  These units sound incredibly bad.  If your signal goes through
one you can tell immediately, really, everything sounds very thin.
There are only a few opamps in the audio path, I don't remember what
kind, and the mixers are spec'd at something like 0.01% distortion,
yet they suck all the life out of the music.  There are other
opamp-based mixers that sound great of course.

On the other hand there are tube amps rated at over 1% distortion that
sound beautiful.

And then there's the Aphex Aural Exciter and the BBE Sonic Maximizer
that intentionally add distortion to bring out certain aspects of the
music.  Okay, that's a reach.  

Other classic examples are the Pioneer and Technics hifi receivers
from the mid-70's distortion spec race.  These companies had marketing
departments that understood that it generally wasn't practical for
their customers perform reasonable listening tests and purchased based
on distortion specs instead.  So suddenly there were receivers on the
market with huge amounts of feedback for a 0.001% distortion spec, and
they sold well but sounded terrible.

   "You know that's not true"
   Howha! That's strong!

:-)  

I was actually trying to point out that our language has a tendancy
to obscure what's really happening.  When we start talking percentages
it not only implies that we're measuring in the same units, but that
our measurements are appropriate to begin with.  

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com