All pass filters?

[Martin Czech]

SNIP
> A certain spectral component of this pulse will be shifted in phase by a
> certain
> amount (which can easily be larger than 360degree). This is equivalent to
> being delayed by a certain time. I even prefer to look at the delay as 1st
> order effect, and phase shift as a derived function. The filter is a medium
> 
> thru which the electric wave propagates, and this medium has a certain 
> speed for the wave to go thru it. This speed is frequency dependent - I 
> think for optical media and light waves it's called dispersion (?). In the
> all 
> pass filter this means that phase and delay are not a linear funtion over 
> frequency.
> 
> So in real life, everything works fine. It's just the Fourier Transform of
> strictly periodic signals which may lead to some confusion.
> 
This is what I also thought. It is usefull to record  the phase response
without (artificial) discontinuities, because we then come to group delay,
I think this is d/dw PHI(w) (w:= ommega). But resonant circuits do have
a phase jump.  Does anybody know, how group delay can be interpreted
there. Infinite?

Just curious.

m.c.