Hello there. I've been studying filters and I was hoping someone could help me figure out some details about the filter objects in Pd. I'm mostly concerned about the filter types such as butterworth, chebyshev, bessel and eliptic.
For instance, in [biquad~], can you get all of these 4 types of filter? I guess so... but if it's true, what are the differences in calculating the coefficients? Or perhaps someone could suggest me somewhere to learn about it.
But like, about the filters described at "Cookbook formulae for audio EQ biquad filter coefficients"
http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
Do any of you know if they're Butterworth or what?
And what about the filters in Pd, I was able to implement with biquad the following objetcs: [lop~], [hip~], [bp~], [lores~] and [reson~]. What types would they be?
I'd also like to hear something about [vcf~].
Well, that's it...
thanks ;)
On 15/12/14 14:49, Alexandre Torres Porres wrote:
Do any of you know if they're Butterworth or what?
I'm not sure how much difference it makes for low-order filters (biquad has 2 poles and 2 zeros). The differences really matter more for higher order filters, say 8 poles or more...
You could waste time calculating coefficients for a biquad cascade (the process is quite involved - see the mkfilter package online), but I'd just use the ones already made in iemlib...
Claude
Hi,
On Mon, Dec 15, 2014 at 03:41:45PM +0000, Claude Heiland-Allen wrote:
On 15/12/14 14:49, Alexandre Torres Porres wrote:
Do any of you know if they're Butterworth or what?
I'm not sure how much difference it makes for low-order filters (biquad has 2 poles and 2 zeros). The differences really matter more for higher order filters, say 8 poles or more...
You could waste time calculating coefficients for a biquad cascade (the process is quite involved - see the mkfilter package online), but I'd just use the ones already made in iemlib...
There's also a 3rd order BW in the docs, if you're interested in the inner workings: 3.audio.examples/H13.butterworth.pd
Ciao
Frank Barknecht _ ______footils.org__
"I'm not sure how much difference it makes for low-order filters (biquad has 2 poles and 2 zeros). The differences really matter more for higher order filters, say 8 poles or more..."
That's really relevant information, thanks :)
I'd just use the ones already made in iemlib...
Sure, but it's more of theoretical doubt and concern. I just wanna learn more about it, even if I just use what's there in iemlib.
There's also a 3rd order BW in the docs
Sure, I know about them and I'm studying it. And I'm also now checking http://msp.ucsd.edu/techniques/latest/book-html/node145.html
I assume it's a matter of how to calculate the coefficients for you to get filters that are butterworth/chebyshev/etc, and the text from miller point to how to get butterworth coeficients. But it doesn't point to how to get Chebyshev 1 pr 2, Eliptic, Bessel and whatever. Any hints?
And I still wonder what's the kind of filter from objects like [lop~], [hip~], [bp~], [lores~] and [reson~] for instance (cause I know how to get those with biquad coefficients). And also about the filters described at "Cookbook formulae for audio EQ biquad filter coefficients" http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
Do any of you know what kind of filter it is?
Thanks
2014-12-15 13:59 GMT-02:00 Frank Barknecht fbar@footils.org:
Hi,
On Mon, Dec 15, 2014 at 03:41:45PM +0000, Claude Heiland-Allen wrote:
On 15/12/14 14:49, Alexandre Torres Porres wrote:
Do any of you know if they're Butterworth or what?
I'm not sure how much difference it makes for low-order filters (biquad has 2 poles and 2 zeros). The differences really matter more for higher order filters, say 8 poles or more...
You could waste time calculating coefficients for a biquad cascade (the process is quite involved - see the mkfilter package online), but I'd just use the ones already made in iemlib...
There's also a 3rd order BW in the docs, if you're interested in the inner workings: 3.audio.examples/H13.butterworth.pd
Ciao
Frank Barknecht _ ______footils.org__
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
So I've been reading all day about this and this is what my intuition tells me:
the filters from the objetcs I mentioned ([lop~], [hip~], [bp~], [lores~] & [reson~]) and the ones described at "Cookbook formulae for audio EQ biquad filter coefficients" are not butterworth/chebyshev/eliptic/bessel/etc. They're just what they are.
Seems these filter topologies are some special cases that don't apply to these more general filters.
Does anyone back this up?
Moreover... I've figured out how to work with butterworth filters. I had the wrong impression you could start from a second order filter and cascade it a few times to achieve higher order filters, but that's not the way it is.
thanks
2014-12-15 15:00 GMT-02:00 Alexandre Torres Porres porres@gmail.com:
"I'm not sure how much difference it makes for low-order filters (biquad has 2 poles and 2 zeros). The differences really matter more for higher order filters, say 8 poles or more..."
That's really relevant information, thanks :)
I'd just use the ones already made in iemlib...
Sure, but it's more of theoretical doubt and concern. I just wanna learn more about it, even if I just use what's there in iemlib.
There's also a 3rd order BW in the docs
Sure, I know about them and I'm studying it. And I'm also now checking http://msp.ucsd.edu/techniques/latest/book-html/node145.html
I assume it's a matter of how to calculate the coefficients for you to get filters that are butterworth/chebyshev/etc, and the text from miller point to how to get butterworth coeficients. But it doesn't point to how to get Chebyshev 1 pr 2, Eliptic, Bessel and whatever. Any hints?
And I still wonder what's the kind of filter from objects like [lop~], [hip~], [bp~], [lores~] and [reson~] for instance (cause I know how to get those with biquad coefficients). And also about the filters described at "Cookbook formulae for audio EQ biquad filter coefficients" http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
Do any of you know what kind of filter it is?
Thanks
2014-12-15 13:59 GMT-02:00 Frank Barknecht fbar@footils.org:
Hi,
On Mon, Dec 15, 2014 at 03:41:45PM +0000, Claude Heiland-Allen wrote:
On 15/12/14 14:49, Alexandre Torres Porres wrote:
Do any of you know if they're Butterworth or what?
I'm not sure how much difference it makes for low-order filters (biquad has 2 poles and 2 zeros). The differences really matter more for higher order filters, say 8 poles or more...
You could waste time calculating coefficients for a biquad cascade (the process is quite involved - see the mkfilter package online), but I'd just use the ones already made in iemlib...
There's also a 3rd order BW in the docs, if you're interested in the inner workings: 3.audio.examples/H13.butterworth.pd
Ciao
Frank Barknecht _ ______footils.org__
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
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Alexandre Torres Porres -
Claude Heiland-Allen -
Frank Barknecht