Josep M Comajuncosas wrote:
> 
> Talking about general filter design routines... I think it would be a nice idea to
> implement a public domain filter design package (Are Meteor or the Pakrs McLean
> free?) in the Csound sources, to be able to design filters from Csounbd itself as
> needed in the filter2 opcode.

I think that's a great idea.
In that case one could also have an opcode which
takes filter-spesifications as an argument, avoiding 
the need to first design filter in an utility-program 
an then using the coefficients with filter2.

maybe something like this 

ar filtgen asig, iftype, ibandtype, iripple, iorder, icorner2, icorner2

where
iftype : filtertype 1=Butterworth,2=Chebychev,3=Bessel
ibandtype : Bandtype 1=Lowpass , 2=Highpass, 3=Bandpass, 4=Bandstop
iripple : ripple in dB for Chebychev filter
iorder : order of filter
icorner1 : cornerfrequency 1
icorner2 = cornerfrequency 2, for Bandpass/Bandstop filters

the opcode would then at inittime design the filter and maybe show 
a graphic output of freq ,phase and impulse response.

at http://www.cs.york.ac.uk/~fisher/mkfilter/ there is an online 
interactive filter design page.
The source code is available to download too, but I haven't found anything 
about license.
If this is interesting one could off course ask the author if it's okay
to use his sources in csound.