Sat Jun 13 21:11:23 EDT 2020

Low frequency non-linear model updates

Running into this interesting problem: frequency calibration of a
synth.  First I attempted a fairly standard integrating regulator,
which really didn't work out, mostly because of the delay on the
frequency measurement.  Then I realized the parameter I want to model
(temperature) is much slower moving, so the idea was to split it up
into two parts:

- a feedforward control based on a model

- low frequency update of the model (e.g. 1/sec) after initial
  explicit calibration.

The model will likely be a polynomial compensating for the
nonlinearity in the system.  This however is temperature-dependent.