[sdiy] long delay lines

[Derek Holzer]

Dear list,

I've been investigating delay lines lately. The "single chip digital 
delay" thread from Jan 2006 on this list was very good reading! I'm 
still a bit of a beginner in this world, but there are some people 
around where I live (Berlin) who can probably help me a bit if it gets 
into the realm of PIC chips and CODECs and the like. But I'd like to get 
a clearer idea of what might be necessary before I go to them for help.

My first question is, are there currently any "single chip" solutions 
for this kind of application? I've been playing around quite a bit with 
the ISD voice recorders, and they're great for "throw away" gadgets but 
not at all what I want for sampling/looping/delays.

The spec I'm aiming for is:

* 16bit sound
* 44.1K sampling rate
* Maximum delay of well over a second...hopefully up to 3 seconds
* Possibility of decaying feedback or stable looping
* Reproducible design (i.e. low number of components, not too expensive 
or time consuming to program), since I hope to make 8-12 of the things!
* Small package (by this I mean that I'd like to construct it on a 
modular synth-sized board...I have a laptop which I currently use for 
this delay system which is quite big enough, thanks!)
* SMD components aren't a problem, I can probably work out soldering 
them by hand or oven somehow

I'm also curious about the relationship between clock time and audio 
quality. Will longer delay times always necessarily loose quality? 
Conversely, if I choose a system where the clock speed is separated from 
the delay time, do I lose the ability to pitch the sound down by 
lengthening the delay?

 From the archives, I understand that there are a few options:

1) Oversampling CODEC + dsPIC + DRAM (44.1 kilosamples/sec * .010s * 16 
bits = total RAM needed in kilobits)
2) DSP chip (w/ CODEC?)
3) ADC + DAC (oversampled) + PIC + DRAM

And I'm sure others that I didn't find. It would be good to know what is 
necessary for programming the different digital interfaces, since that 
may determine what kind of chip I will use in the application (and 
possibly which of my friends I can recruit to program it!).

Can anyone who has taken up a similar project send me some pointers? I'm 
aware that my "spec requirements" will require some flexibility, of course!

thx+best wishes,
d.

-- 
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 198:
"Instead of changing the thing,
change the world around it."