Multipath Filters

[mbartkow at ET.PUT.Poznan.PL]

Please note that the feedthrough is only a problem in such cases where we
want to avoid hearing the clocking signal. General filtering applications,
esp. in measurments are such cases, but it is not neccessarily so in syn-
thesizers. A very nice application of the n-path filter as a synth module
involves taking the clock from another VCO which is in some harmonic rela-
tion to the signal feeding the input of the filter. This is the same situ-
ation as e.g. frequency shifters which generally produce out-of-tune sounds,
but driven from a second VCO reward with beautiful clangorous, yet 
"playable" sounds.

I have not built the filter yet, but I would expect to hear something similar
to deep audio rate frequency modulation of "normal" filter cutoff. So _maybe_
this is less exciting. But on the other hand there is a lot left for wild
experiments. Imagine each path in the filter featuring deliberately *different*
capacitor or even a more complicated LRC network. Now imagine deliberate unba-
lancing the switching waveform by aplying different PWM waves to control
the switches. In a simplest case of 2-path filter one may achieve drastic 
changes of the total response by changing the ratio of the two different 
branches being switched on.


regards,

MB


--

Maciej Bartkowiak, PhD
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