A simple way of creating the type of effect described in the Bode patent:
– Sum input signals to mono
– Run through 6 or more 1st order allpass filters in series, with the coefficients set to a pleasant sounding area, usually fairly close to the unit circle.
– The series allpasses feed a phase-differencing based frequency shifter. FIR based frequency shifters can work, but don't have the built-in phase wiggles of the IIR based frequency shifters. The "classic" frequency shifter feedback effects are based around 12th order IIR Hilbert networks, where there is a considerable amount of phase lag.
– One of the outputs of the phase shifter is scaled and fed back into the input of the allpass filters.
– The system is mixed with the original input signal as needed.
If you replace the series allpass filters with a short delay line, you can get a "barberpole flanging" sound.
It seems like it would be fairly easy to wire such a system up in Vsig. I've built similar networks before in Csound, Reaktor, and MAX/MSP, with my latest realization (ValhallaFreqEcho) done in C++.
Sean Costello
