I think this is a fantastic idea. It might also be interesting to create a
general-purpose filter design program in Java, so all platforms can use it,
that would format the filter coefficients into a line of Csound orc code for
filter2.

-----Original Message-----
From: Roger Klaveness 
To: csound list 
Date: Friday, January 29, 1999 4:30 AM
Subject: Re: TB-303 like Lowpass-Filter


>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.
>
>Roger K

As usual, the devil is in the details. I used the filter design page to
generate some of the coefficients I used to test filter2 for IIR filters.
The filters work fine in infinite-precision math but fail miserably in
Csound's single-precision math. I agree that the proposed opcode would be
most wonderful. However, whoever does it is in for some tedious work in
finite precision arithmetic.

At 9:28 AM -0500 1/29/99, Michael Gogins wrote:
>I think this is a fantastic idea. It might also be interesting to create a
>general-purpose filter design program in Java, so all platforms can use it,
>that would format the filter coefficients into a line of Csound orc code for
>filter2.
>
>[stuff deleted]
>>
>>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.
>>
>>Roger K


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