[sdiy] 20ms delay? analog allpass filter?

[René Schmitz]

Am 08.02.2023 um 14:47 schrieb Tom Wiltshire:
> I had a go at this problem using two DG406 1-to-16 switches and an AS3360 dual VCA to provide crossfading from one signal to the next. The relevant 4-bit addresses and two VCA CVs were provided by a PIC. For the delay, I used the LC delay line that JH designed for his Hammond Scanner project.

Yes, by using the switches and a crossfader, you can have it crossfade. :)

> It worked, but there was a notable volume modulation at the scanning frequency because I didn't get the crossfade to be equal power. The CVs were simple linear ramps, but there needs to be another lookup table stuck in-between so you get a sin/cos cross fade to make it smoother. At least, I *think* that's where the problem came from.

If you listen to the examples, that is also very present in the Hammond 
scanner. Look at the geometry of the plates, it looks like its doing 
linear crossfade. (If that is desirable to have is a completely 
different story.)


Best,

  René