[sdiy] 4xD Audio Samples [was: BBD clock circuit]

[Seb Francis]

Antti Huovilainen wrote:
> On Fri, 18 Aug 2006, Seb Francis wrote:
>
>> I wasn't sure the pitch shifting delay modulation thing could be done 
>> well in digital
>
> If the modulation is relatively slow (read: not audio rate), you can 
> use allpass fractional delayline. Google for "Jon Dattorro" and grab 
> "Effects Design pt2: Delay-Line Modulation and Chorus" from his homepage.
>

Looks like an interesting document.  The method I've used is basically 
what he describes in the section "4 Linear Interpolation".  I keep the 
input buffer moving at a constant step of 1 sample per sample and change 
the output buffer step in order to 'catch up' to the new delay time 
within the period of the new delay time.  Linear interpolation (with no 
filtering) is used to get the output samples.  And actually it sounds 
very good.  I've limited the resampling amount to 5 octaves so any 
really big delay jumps take slightly longer than the new delay time to 
settle to the new time.

I also have a non-resampling mode where the delay time is just switched, 
but only at a point where the audio levels match fairly closely - this 
avoids clicks and works well for relatively shallow, slow modulation.

Some audio samples are online here:
http://burnit.co.uk/sdiy/index.php?page=4xd&subpage=audio

Seb