Digital controlled filter.

[Ingo Debus]

The Dark force of dance wrote:
> What about zipper noise etc?

Can't say much about this, because in the application I used it, cutoff
was only changed when there was no signal at the input.

However, the opamp input in the "digitally controlled integrator" sees a
different impedance for each digital value of the DAC, especially there
are huge differences in the range of low values (1, 2, 3...). This may
lead to jumps in the output offset voltage of the filter unless a FET
input opamp is used.

Ingo