[sdiy] digital delay, was ...

[Harry Bissell Jr]

Hah... since I am the worlds foremost proponent
of BBD circuits... I'll suggest how to do this
(ROTFLMFAO)  ;^P

Make a VCO that has a real frequency for zero volts
and send an FM signal through the BBD. The CV is
represented as frequency and the delay is the BBD
clock. If you used sine waves... I think you could
do away with most of the anti-alias filters as well.

Use a tachometer circuit for 'slow response' CV
recovery... or a PV-1 Pitch to Voltage converter
for faster response (two cycles of the FM
frequency...)

H^) harry



--- eq927 at freenet.carleton.ca wrote:
> Using a BBD to delay CV's not as easy as it may
> appear...
> 
> Problems are that:
> a) BBD input needs an offset voltage to work
> properly, therefore audio 
> rides on top of the offset. DC signals would require
> subtracting out 
> this offset at the other end of the BBD but...
> b) this offset varies with clock rate...
> c) the Panasonic databook shows a differential
> method for cancelling out 
> this variable offset using both halves of a dual BBD
> chip - if separate 
> BBD chips are used, they will need to be matched
> over the range of clock 
> rates used.
> d) another method would be to make some sort of
> processor which creates 
> a compensation voltage dependent on clock rate.
> 
> Probably best to use a simple A/D> shift register>
> D/A for delaying 
> CV's. Some of the simple digital delay chips might
> also be useable. If 
> the CV's change slowly enough lowpass filters at the
> input might not be 
> required. Maybe aliasing the slowly changing CV's
> would produce some 
> good sounds when fed into VCO etc.
> Regards, Mike