[sdiy] digital delay, was ...

[eq927 at freenet.carleton.ca]

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