The audiophile∗ version: make it 24 bit and give it a fairly high
base sampling rate (96 kHz?), so you could sweep down to half
the base SR and up to double (with 192 kHz capable parts) and
still use a fixed full audio bandwidth anti-alias filter? Linear
voltage control and/or exponential for the for the physmo stuff?
Manual selection of taps would be excellent. You could have
multiple taps by digital mixing and/or multiple DACs. The same
basic module could be optimized for longer or shorter delay
times. Problems: expense, jitter, RFI - but, could it work?
∗From my understanding and experience, this is what it would
take to get close to high end analog (MOTM quality?) with digital.
Barry
--- In motm@y..., "paulhaneberg" <phaneber@o...> wrote:
> 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.