format filter bank/string filter

[jhaible]

> Anyone got some schematics for these multiple bank chorus units. My RS-09
> which I sold many years ago had a great analogue one, bit noisy mind. I
> built a full stereo one with two TDA1022s, but it was a very much trial
and
> error getting the time delay right and adjusting the right amount of
> feedback and feedforward. It does sound good, but it would be nice to see
> how the experts did it. I have a copy of Tim Orr's one published in ETI,
it
> has a log convertor to drive the high frequency VCO from the triangle
LFO. I
> found that sines were the best in mine.


What you will want for a "typical" String Ensemble chorus is 
3 short BBD delay lines and two 3-phase LFOs.
One LFO is approx. 0.6 Hz, the other one approx. 6 Hz.
Both LFOs have 3 different outputs with sine waves that are 120 degrees
apart from each other.
Each BBD line is modulated by the sum of two LFO outputs:
BBD1 modulated by LFO1 (0 degree)  + LFO2 (0 degree)
BBD2 modulated by LFO1 (120 degree)  + LFO2 (120 degree)
BBD3 modulated by LFO1 (240 degree)  + LFO2 (240 degree)

JH.