Digital delay (was MN3005, MN3007)

[Harvey Devoe Thornburg]

> 
> Jeremy Brookes <bluebear at enterprise.net> wrote:
> >>The infinite delay is not practical realizeable without a kind of
> >>compression. You could dial the feddback only close to infinity, on one
> >>side the signal would slowly fade, on the other it wold rise and rise,
> >>until total distortion/and or oscillation. I think it needs a jard limiter
> >>before the delay to get a real infinite delay without this problems.
> >

I think your limiter is more or less a degenerate case of a compressor 
with infinitely fast response times. As such, it has the most tendency to
distort the output.  As long as the compressor's time constant is on 
the order of the delay period there should be no problems using a
compressor.  I have gotten very convincing Roland space-echo sounds 
with a compressor and high-pass EQ in the feedback path.

> >
> >The infinite repeat was from Michael Rogers who was referring to a DOD
> >digital delay pedal. Being digital I guess it would be quite easy for the
> >feedback to be in the digital domain, whereas the compressing and expansion
> >only apply to the analogue input and output, not the feedback loop. Or I
> >might be wrong :)
>

If audible distortion is what you want, then I'd think you'd want the
feedback compression in the analog path; if you do this digitally, 
you'll have to upsample by quite a bit to avoid aliasing.  This 
problem is worsened with a highpass filter in feedback.  If the compressor
has slower time constants then I've found no problem with doing 
feedback digitally.  The modulation of the feedback signal is not 
enough to generate aliasing.  Plus, there are the advantages of
digital control.

--Harvey