Reverbing

Wavefolding (FM) Delay Lines

Wavefolding effect with a self modulated delay line .The signal is split. One line enters the audio delay line, the other is compressed to a steady voltage range and sent to frequency modulate the clock of the delay line. Adding a feedback control and mixer gives a reverbesque effect, similar in practice to a mechanical spring. One side effect is that the compressor ripple creates small pitch fluctuations which makes it seem a bit too artificial. 

On the computer-in SpinCAD, i tried pitchshifting the signal and using that to modulate the unshifted delay. This sounds promising but it playedback with quite alot of noise on the program. I put this down to how a programed delay works. When you adjust delay time on a programed delay your moving your posistion on the register.  (ADDR_PTR) With A PT2399 or BBD your adjusting the clock speed. Any audio rate modulation seemed to come out fuzzy with the digital apparatus whereas with an analog delay I can get good clean FM with high audio rates.

Belton Brick

Inspired by this belton patent I tried a few variations of a PT2399 reverb. https://patents.google.com/patent/US8204240B2/en

Reverb Tank

This a variation of the belton tank. I've added instead the lfo from the mind warp to tickle the first delay and a high pass distortion with clean blend feeding the tank. Maybe effect loop before the reverb would be nice.

One problem with this tank setup is that you get peaks of resonance. To get high density with a flatter frequency response I need allpass filters to change the phase angle after each delay stage. Keith Barr (Alesis-SpinSemi) provided a nice schematic explaining his basic method. http://www.spinsemi.com/knowledge_base/effects.html#Reverberation

"This loop is composed of four blocks of 2 allpass filters and a delay, although any of the blocks could contain 1 or 3 or more allpass filters, and the loop could be 2 or 3 blocks instead"