Yes, the legendary SID chip was a digital oscillator followed by an analog filter.
After seeing this heroic SID chip reverse engineering (0), I tried building the filter section using a quad opamp to make the state variable filter. It sounds kinda nice for such a simple circuit.
I've been planning a project of using a micro controller to do the oscillators and then use the PWM outputs to drive the filter control voltages.
A passive filter (if you've got the headroom) doesn't have to be fancy ... just a capacitor and variable resistor will let you custom-mellow the excess highs. (Old radios had these for 'tone control' ;-)
