[sdiy] group delay (of filters) and listening

[Czech Martin]

Some (audiophile) publications make a big fuss about group delay distortions.
For us it could be different to investigate differences of filters due to this property.

I have done some experiments on this.

Test signal were:

-solo drumset
-sine bursts
-narrow clicks

All signals are only a few seconds long.

They where fed through a digital allpass filter. The lower frequencies
had a larger group delay then the higher frequencies.
The output was listened via headphones, direct A B comparison of processed
and original data.

The experiments are not finished. Different allpass frequencies have to be tried,
also lagging and leading high and low frequencies.

But it seems that small group delays of up to 1ms are absolutely NOT
audible. E.g. a single real pole 1st order allpass signal can
not be distinguished from the original.
A 3ms difference tended to change the timbre allready.
This is quite contrary to the waveform, which will alter with much smaller
group delays.

This is a bit surprising for me.
This would mean that group delay is not an audible property for most
digital or analog filter designs and applications, except in extreme cases (ringing).

Any comments?

m.c.