[sdiy] Moog filter maths

[Theo]

Why do pp always ask for the good stuff to be off list?

Anyways there is some code for moog filters online.
Just do a web search for "dsp moog filter" or "moog filter code"
The ones I found where not a real model of the moog filter,
but a 24dB filter tweaked to sound like a moog filter.

When you change the resonance or the cutoff,
a bunch of coefficients need to be recalculated.
All the examples sheared one feature;
*( try different values for this parameter till it sounds good )*

The problem seems not to be the moog ladder, but VCF in general.
>From resent discussion on the music-dsp list it seems many DSP pp seem to
think a analogue filter is just some poles and zeros.
Do a bi-linear transform and your set.
Maybe add a distortion behind the filter, cause analogue does distort.
But whatever you do, don't even think of the possibility that the nonlinear
part should actually belong to the filter model itself.

BTW, some of the moog filter code I found was a lot better in this respect.
However it is no where near a model in the sense that the effects of the
individual components are modeled.
More a black box idea, output sounds a (bit) like a moogfilter, don't care
how its done.
Also doesn't walk like a duck, but quacks like a duck, so call it a duck
anyway.
(and never mind the quack sounds more like "woof")

Just some thought,
so math-geeks, get your gun and shoot me ;)

Theo



From: Paul Maddox <Paul.Maddox at wavesynth.com>

> Dear all,
>
>   Is there anyone who's been mad enough to do the maths for the moog
ladder
> filter?
>
>   Im learning DSP, and Ive been told its impossible to do in a DSP..
>
>   I take the word impossible as a challenge!
>
>   Probably best to reply off list :-)
>
> Paul
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