[sdiy] group delay (of filters) and listening

[Don Tillman]

   > Date: Tue, 5 Oct 2004 13:40:05 +0200
   > From: "Czech Martin" <Martin.Czech at Micronas.com>
   > 
   > After all, it is not important how the group delay was achieved,
   > but only it's shape.

Oh?  Are you sure?

I'll claim that group delay is not an actual physical phenomenon, but
an interpretation of phase measurements.

(If you have a device that provides a small delay without any other
side effects or distortions, if you measure the phase of the output,
compared to the input, you'll see the phase changing with frequency,
linearly.  There's no "phase distortion" going on, the resulting
waveform looks identical to the original waveform, it's just delayed a
little bit.  Group delay is an attempt to interpret phase measurements
in this light, as a delay that that changes with frequency.)

But a measured phase value could be due to any number of mechanisms;
from a direct signal, from an inverted polarity signal, from a delay
line, from a simple filter circuit, from a multiple stage filter
circuit that shifts the phase and delays the signal, or from any
combination.

These will all carry different sonic artifacts.

  -- Don

-- 
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com