[PD] [vcf~] and [biquad~] filters

julien.breval at tremplin-utc.net julien.breval at tremplin-utc.net
Tue May 18 14:49:15 CEST 2004


> why don't you use then filtergraph~ to get all biquad coefficients?
> you can specify both F and Q and it will feed your biquad with the
> required list of coeffs.

I tried it of course, but the shape of the original bandpass filter in 
[filtergraph] is not what I am looking for. It's too complicated, the curve has 
at least three very significative courbure change points (it looks looks like a 
gaussian curve, with a "fat" base). The quality factor is only significative 
over -3 dB ! This means that too many frequencies are kept, even if you raise 
Q. This makes this filter almost "wha-wha" sounding (or too much "resonant").
I assume most electronic musicians like this "analogue" sound. 
 
I personnaly only want a quasi-spike (or isoceles triangle, if you prefer), and 
no resonance nor wha effect. I know the actual curve will be a bit concave, but 
that's not a problem actually.

Any links to (free) external filters or abstractions related to filters under 
MSP ?
Why didn't they use [vcf~] instead of [reson~] ?

I still wonder why there are no conversion formula on the Internet. I think I 
will get into the equations directly to solve it myself (maybe using Scilab). 
Has anyone got into it there ? 


> On Tue, May 18, 2004 at 12:35:40AM +0200, julien.breval at tremplin-utc.net
> wrote:
> > Selon Frank Barknecht <fbar at footils.org>:
> > 
> > > Hallo,
> > > julien.breval at tremplin-utc.net hat gesagt: //
> julien.breval at tremplin-utc.net
> > > wrote:
> > > 
> > > > The right solution sould be to use [biquad~]. MSP-[biquad~] looks
> like
> > > Pd-
> > > > [biquad~] with some arguments inversed. 
> > > > Unfortunately, besides a paper from Harmony Central I didn't find much
> 
> > > > information on it. Do you know any documentation about biquad filters
> ?
> > > 
> > > Guenther wrote a set of externals to assist in biquad~ filter design.
> > > See externals/ggee/filters on the CVS at pure-data.sf.net
> > 
> > Thanks, I will have a look at it
> > 
> > actually, all I need is some basic conversion information from (F, Q) to
> the 
> > the parameters of [biquad~]
> > 
> > 
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