Thanks for all the replies. You answered my question and then some Florian! I think I will give the RS-120 a miss and go with the A-188-1 and A-106-6.

Thanks,
Jonathan

--- In Doepfer_a100@yahoogroups.com , Florian Anwander <fanwander@...> wrote:
>
> Hi Jonathan
>
> > Sorry, i meant comb filter.
>
> comb filters are based on the principle of phase cancelation around a
> certain frequency. They can be achieved by many different means:
>
> 1.) Each analog filter does a phase shift around the center frequency.
> For example: a multimode filter like the A121 does this: if you mix the
> high pass and the low pass, you will get a notch-filter, which one may
> regard as a single notch comb filter. If you would add several
> multimodefilters at different center frequencies, you would get a multi
> notch comb filter.
> 2.) This kind of a "multi notch comb filter" can be achieved more easily
> using several stages of so called allpass filters, which in fact do not
> filter at all, but they still do the phase shift around their center
> frequency. If you mix this "filtered" signal with the original signal
> you will get again a comb filter. If you modulate the center frequency
> of this chain of allpass filters you will get what we call a "Phaser".
> 3.) A different approach is the usage of a delay line. A delay will
> cause phase cancelations at certain frequencies, if the delay time
> corresponds to the wave length of this frequency. If you modulate the
> delaytime you will get what we call a "Flanger".
>
> These three cases differ by the position of the notches in the frequency
> spectrum
> In case #1 it depends on the different center frequencies of these
> filters, which could be selected free (in theory).
> In case #2 it is spread in linear steps over the frequencies (e.g. 200,
> 400, 600, 800... Hz).
> In case #3 the notches appear each doubling of the frequency (e.g. 200,
> 400, 800, 1600 ... Hz).
>
> Florian
>