Digital controlled filter.

[Ingo Debus]

The Dark force of dance wrote:
>         Anyone know of a readily available digitally controlled filter. I was
> hoping for a VCF type filter which can be run in band-pass and Low-pass
> modes but was controlled by a serial digital input. I2C/microwire/etc. I

How about building a state variable filter with opamp integrators that
have a multiplying DAC instead of a resistor? There are dual, quad and
octal multiplying DACs with serial control available. Since the
impedance matching of dual/quad/octal DACs is good but the absolute
impedance tolerance is rather poor you must use the DACs from *one* chip
for a filter. If you need absolute accuracy of the filter you'll have to
select the caps for each DAC chip.
I built several filters that way (not for musical applications), works
fine.

Ingo