[Switchable ladder filter]

[Sean Costello]

Harry Bissell wrote:

> The other point is where you get the resonant feedback from. I got the best
> (simulated) results from taking the feedback from the last stage at all times,
> and tapping the filter with a differential amplifier at an earlier stage....

It would seem that you would get more powerful control over the sound if
you could choose where the tap point for the feedback is, as well as the
output taps. While testing out my new phase shifting opcode for Csound
(allpassn - lousy name, but what would be a better name for n number of
single-order allpass stages? Suggestions welcome), I experimented with
different tap points for the output and the feedback. Invariably, the
feedback tap dominated the sound. If there were 8 stages before the
feedback, but the output was tapped after stage 4, the sound was far
closer to a standard 8 stage phaser. An 8 stage phaser with the feedback
tap taken after the 2nd stage (like the Schulte Compact Phaser 'A')
sounded very nice, with some swirly complexity, but none of the
overbearing "fruitiness" that an 8-stage phaser can display.  I don't
know if this is true with the Moog filter, but I have a feeling that it
would be.

Sean Costello