Filter design musings...

[Rob01]

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> From: Martin Fay <mfay at fs2.cp.umist.ac.uk>
> To: synth-diy at horus.sara.nl
> Subject: Filter design musings...
> Date: Friday, March 28, 1997 8:00 AM
> 
> I've been playing with some digital filter algorithms for my synth 
> simulation program and this thought occured to me:
> 
>   The character of a filter is more dependant on the nature of the 
>   resonance response (i.e. feedback loop) than the cutoff slope.
> 
> For instance my late-model Odyssey has a fairly narrow resonance 
> bandwidth, while a BassStation has a much wider bandwidth, and they 
> end up sounding very different.
> 
> What do you all think?
> 
> 
> Martin
> 
>	Actually, Martin, i believe that the filter response of the Odyssey
at high Q exhibits a phase shift and that accounts for the loss in freq 
response because the current and voltage are no longer in line.. Ive
noticed impedance changes on the output signal of my Odyssey at high
Q.. I would also venture to say that the total output changes as the Q
changes, but for the most part, the Odyssey filters are TOO good at 
their job, and that is why the unit is such a strange noisemaker, because
the
filters sound completely alien and "unreal". PLUS at high Q, i believe that

the input voltage becomes stressed and some of the VCO noise starts to
seep into the filter ground, making the filter "sputtery and whistle". I
think, on
the other hand, the Basstation sounds like it has a very weak lower filter
slope at high Q, and a pretty steep upper slope...So, most of your highs 
are present, almost ALL of your lows are there, and the filter has
tremendous
gain, so it gets pretty damn loud and unruly, as youve prolly noticed..
Dont
use one live without a compressor!!! 
my 2 cents
Rob01 
:>