On Sat, 19 May 2007 10:03:27 +0100, Jim Lesurf
wrote:

Your description would be more appropriate for a 'nulling' or cancellation
method where two sources are employed. But need not involve any feeback.
In the context of this thread, this distinction is relevant as the
'dynagroove' system was a method which tried to cancel or null one
distortion with another - but this involved *no* feedback mechanism
to compare the two in reality. The LP cutting system had no way to
sense what the LP replay system would actually do when playing the
LP.


This is pre-distortion. It is currently widely used in RF power
amplifiers to lift the third order intercept point sufficiently to get
acceptable output power from RF power transistors, which are notorious
for their "soft" transfer characteristic. GSM wouldn't be economically
possible without pre-distortion.

The transfer curve of the power amplifier is measured, and then one of
two things happens. If the solution is a hardware one, a matrix of
diodes and resistors is designed to straighten the overall curve.
Alternatively in software, the lookup table for the DAC that creates
the signal is changed to oppose the errors of the power amp.

d

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Pearce Consulting
http://www.pearce.uk.com