MOTM

I've been playing around with ideas for delay modules for some time.
I would use a ADC of presumably 16 bits or better on the input with 
a fixed filter at around 20 kHz.  The converted data would go into 
RAM of a fixed length then come back out through a DAC and another 
filter.  Most delay lines vary the point at which the data comes out 
of RAM.  This is why you get zipper noise when varying the delay 
time on most digital delays.  In order to do away with the zipper 
noise you have to vary the clock speed.  You would want to do this 
with voltage control.  I'm not sure if you'd want the frequency 
response of the clock to respond linearly or exponentially or 
logarithmically to the control voltage.  A selection of all three 
would be interesting.  The problem is (and I don't know the answer 
yet) Over what range can you vary the clock rate of the converters 
and RAM?  This is something I'll be playing with in the future if I 
ever get caught up on module building and get started on some of my 
own ideas.  It doesn't sound cheap though.
I agree that you can do a lot of interesting things with short delay 
times.  Although most delays do not go below 1mS you can do some 
great stuff in the 50uS to 1mS range.  One of my favorites is to 
split a mono signal and delay 1 side my a sub ms amount.  Great for 
really strong stereo imaging.
I think you would want the feedback as well.  Ideally, I'd make the 
feedback amount Voltage Controlled with a VCA.
Interesting Stuff.