A better description is that it compares the input with the output and
adjusts the system to reduce discrepencies. Thus it changes the effect of
any nonlinearity within the loop. It doesn't do this by using "another"
form of distortion as a comparison for "offset".

I was thinking of the Texan amplifier. It uses really cheap 747 op-amps
and a hefty feedback mechanism so that the output waveform is all but
identical to the input waveform (except in amplitude).

If you were to listen to the intermediate stages, you'd probably be
aware of all sorts of horrible distortions (the 747 never claimed good
linearity). So in the middle (between input and output stages) you have
distortion, and the negative feedback introduces and equal, but opposite
amount of distortion and feeds it into the -ve input of the input stages
747.

One fascinating aspect of the design was that the volume and tone
controls affected only the feedback loop. In effect, the wrong volume,
or a lack of treble was just another sort of error that had to be corrected.

I suspect we should be in alt.semantics :-)

--
Steve Swift
http://www.swiftys.org.uk/swifty.html
http://www.ringers.org.uk