[sdiy] group delay (of filters) and listening

[mirwin at qouest.net]

Martin (and list),
I have done some experiments with long allpass chains (including up to 
24 first-order analog allpass stages, identical sections). If you listen 
to a narrow pulse (say one millisecond) the non-constant group 
delay (dispersion) is quite obvious - the "click" turns into a short 
"blip" with rapidly descending pitch. The effect on recorded music is 
much less obvious, more so with fewer allpass stages. 
Mike