All pass filters?

[Ethan Duni]

>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 (?).
-yes, it's called dispersion.  incidentally, the optical and electrical
effects are the same thing, so the term holds for all media.  the project
i'm working on at work uses media that are dispersive and "nonlinear" (here
meaning that electricity propagates more quickly depending on its
instantaneous value).  this 'nonlinearity' alone reults in shock waves (the
top of the wave catches up with the front), but in a media that is also
suitably dispersive, it gives rise to what are called solitons, which are a
very peculiar kind of solitary wave.  what this all translates to is that
devices can be developed wherein you put a pulse in one end and get a train
of waves out the other (in my case we're feeding it big pulsed power and
getting high-power RF out the other).  i hope to develope a lower-power
version suitable for use in a synthesizer or something at some point.

Ethan