[sdiy] long delay lines

[Seb Francis]

Hi Derek,

Derek Holzer wrote:
>
> I've been investigating delay lines lately. The "single chip digital 
> delay" thread from Jan 2006 on this list was very good reading!

I have a feeling it was me who started this thread back then.  As it 
happened I didn't ever find a single chip solution that satisfied my 
requirements.

This is what I built in the end:
http://burnit.co.uk/sdiy/index.php?page=4xd

It's based around a dsPIC, CODEC & SRAM (actually x2 as I wanted 4 delay 
channels, and I added another PIC to control the UI for everything).

It uses a constant sampling rate (modern CODECs do not respond well to 
widely varying the sampling rate), with different delay times achieved 
by changing the buffer size.  It has a mode that when the buffer size is 
changed it resamples the audio in the buffer in realtime until the 
buffer pointer catches up with where it needs to be.  This gives a 
similar effect to a BBD based delay while the sample rate is varied, but 
still maintains 16bit/48kHz quality whatever of the delay time.

The internal maths for the realtime resampling is extremely simple but 
it turned out to sound very good.  There are some audio samples on the 
website.

Seb