Doepfer

Hello

> Now: isn't the phase shift of this shifted signal, due to the
> physical effect of passing through some sort of filter (something
> like notch or BP)?
No.

What we call a "filter circuit" is a circuit which has two 
characteristics, which are both related to the center frequency, and 
which change above and below the center frequency.
1.) The phase of the output signal in relation to the input signal
2.) The level of the out signal in relation to the input signal

In both cases this is not an abrupt change, but the change starts slowly 
somewhere below the center frequency and ends somwhere above.
Both characteristics change at "the same time".

We know five kinds of filters: Lowpass, Bandpass, Notch, Highpass, and 
Allpass

All of them have the phase behaviour in common.

But only four of them have the level behabviour in common:
* Lowpass: the output level above the center frequency is less than below
* Highpass: the output level above the center frequency is more than below
* Bandpass: the output level around the center frequency is more than 
below and above
* Notch: the output level around the center frequency is less than below 
and above

The allpass does not change the level, but still changes the phase.

You could use e.g. a Lowpass also for a phaser, but since there is also 
this level-thing, the phaser effect would stop soon above the center 
frequency: one ocatve above the center frequency there is nothing to mix 
with the input signal anymore - it is filtered away already. Same for 
all other types of filters. With exception of the allpass: The allpass 
provides the wonderful phase shift, wothout spoiling the game by muting 
the shifted frequencies.

A phaser works only with an allpass - nothing else. But the other way 
around: a phaser never can be used as a filter.

Florian