I'm pending to say that there is no real distinction between "Resonant filter" and a "resonator", and a "bandpass" can be implicitly thought of as a resonator. Here's what I also found in Julius' website
https://ccrma.stanford.edu/~jos/filters/First_Order_Complex_Resonators.html Pass the mouse cursor over the "Resonator" over the title "First-Order Complex Resonators <https://ccrma.stanford.edu/~jos/filters/Two_Pole.html>" to see the popup (also attached). cheers 2015-01-13 1:20 GMT-02:00 Martin Peach <[email protected]>: > I was looking at circuit diagrams for analog synthesizers recently and > noticed that the "resonance" control is nothing more than feeding some > fraction of the output back to the input. With more feedback oscillation > occurs at the cutoff frequency for any type of filter, highpass, bandpass > or lowpass. > > Martin > > > On Mon, Jan 12, 2015 at 9:09 PM, Alexandre Torres Porres <[email protected] > > wrote: > >> Nice I give an impression to be an expert, but filters is just something >> I've actually recently started studying :) >> >> > I'm wondering if by "resonant" filter you mean the >> > same thing as "resonator" filter? >> >> Now you got me... good question, and I'm not sure, haha. The link looks >> nice btw, will definitely check it. Thanks. >> >> So now I'm even more confused. Is "resonant filter" and "resonator" two >> different concepts? Maybe I'm having trouble with the english nomenclature >> and everything. >> >> To be honest and more detailed about the issues I'm encountering, I ask >> this based on another topic I was discussing with Julius Smith in the >> Supercollider list, but it went dead and I got no replies. In it I was >> asking if the object "Resonz" should really be called a "Resonant filter", >> because it was just a bandpass filter in my opinion. Then Julius was >> mentioning how "*A resonator is a special case of a passband filter >> having a nearly zero-width passband.*" >> >> I see he used the term "resonator" and not "Resonant Filter" (as Resonz >> is described). So yeah, now I'm more confused... is resonator the same as >> resonant or what? >> >> But anyway, we can bring the discussion into the Pd world, and talk about >> the [reson~] object, as I will do later on. >> >> I was googling and saw how the term resonant filter could be used to >> describe a regular bandpass filter. And how the bandpass' center frequency >> could also be called "resonant frequency". So they might be used in the >> same way... (accurately or not). >> >> Now here is my opinion. Just like a resonant low pass filter (the >> [lores~] object in Pd), the concept of resonance in a filter relates to how >> it adds gain around the resonant frequency. >> >> In the Audio-EQ-Cookbook (link: >> http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt ) that presents >> formulas for biquad coeficients you have two different bandpass filters, >> lets call them BPF1 and BPF2. So, BPF2 has "constant 0 dB peak gain", >> meaning it doesn't affect anything arounf the center frequency. Now BPF1 >> says it has "constant skirt gain, peak gain = Q", meaning that the Q or >> bandwidth controls the gain of the filter. I consider BPF2 to be a >> regular bandpass filter, whereas BPF1, which adds gain for narrower >> bandwidths, seems to be a "resonant" one... (which makes me think Resonz >> shouldn't be described as resonant filter, as it's just a bandpass, or >> "BPF2"). >> >> Oh, there's another term around, the "ringing" filter, which seems to be >> another term for resonant filter. In SuperCollider they have Ringz, which >> was supposed to be the same as Resonz object (or a resonant filter for that >> matter), but they are different like the two different kinds of bandpass in >> the EQ Cookbook (Ringz = BPF1 / Resonz = BPF2). >> >> Coming into the Pd world we can talk about the [reson~] object. As the >> name implies, it is a resonant filter. But the helpfile says it is a >> "Bandpass >> filter" (damn). Funny enough, in Max, the [reson~] object is said to be >> indded a *Resonant Bandpass Filter*. So maybe we should update [reson~]'s >> help file in Pd... But the deal is: [reson~] is actually a bandpass like >> BFP2 or Resonz, but it has a separate parameter for the gain. Meaning it >> works basically as a bandpass filter, where changing the Q doesn't affect >> the gain. But you can also give it a boost or a cut with the gain >> parameter. By giving it a boost it would behave in a way that I'm >> considering to be an actual "resonant" filter. >> >> Now let me go ahead and share a patch that I'm writing for my computer >> music classes. It's about several filters that can be obtained with biquad. >> So I present Pd's vanilla filters such as [lop~], [hip~] and [bp~]. I also >> present externals like [lores~] and [reson~] and I do present all the >> filters from the Audio Eq Cookbook as well. It's in portuguese, and part of >> a big series of examples, but what the hell... >> >> By the way, I was also able to implement Resonz and Ringz as [biquad~] in >> Pd, but I don't have it on this example (but to hell with supercollider >> already, hehe). >> >> So there you can check the behaviour and differences that I've pointed. >> For [reson~], I have two separate parameters, one is for "Q", and the other >> one, which is originally "gain", I'm calling the "resonance" parameter. >> Much like the resonance parameter in [lores~]... >> >> As for the Cookbook filters, BPF2 is what I'm calling a regular >> "bandpass", and it has a parameter of "Q". As for BPF1, I'm calling it a >> "resonant filter", and it has a parameter of "resonance" instead of "Q" >> (but the idea is that more Q gives more gain/resonance). >> >> I hope I'm clear in the midst of so much detail and information. It's >> just a stupid doubt on the nomenclature of filters, but this kind of issue >> can be quite a pain in the ass, and the subject of many confusions. >> >> So, in short, I still keep my original question: Are bandpass and >> resonant filters the same? Or is there a difference between calling one a >> resonant and not a bandpass? Moreover, what about a resonator? Is my >> assumption on how to call one a bandpass and a resonant correct or it >> doesn't have anything to do with the official literature? And how about >> what Julius Smith had to say? >> >> Cheers >> >> 2015-01-12 20:03 GMT-02:00 Brian Fay <[email protected]>: >> >> Based on your posts in this group, you definitely know more about filters >>> than I do, so I don't really have an answer to this question - but I'm >>> wondering if by "resonant" filter you mean the same thing as "resonator" >>> filter? >>> >>> I saw something interesting earlier today about using resonator filters >>> as control sources for FM synthesis: >>> http://tai-studio.org/index.php/projects/sound-programming/complexres/ >>> >>> The paper that is linked in the article has some details on the >>> mathematical implementation of the filter, but that's mostly mumbo-jumbo to >>> me. >>> >>> On Mon, Jan 12, 2015 at 4:24 PM, Alexandre Torres Porres < >>> [email protected]> wrote: >>> >>>> Hi, are bandpass and resonant filters the same? Or is there a >>>> difference between calling one a resonant and not a bandpass? >>>> >>>> thanks >>>> >>>> _______________________________________________ >>>> [email protected] mailing list >>>> UNSUBSCRIBE and account-management -> >>>> http://lists.puredata.info/listinfo/pd-list >>>> >>>> >>> >> >> _______________________________________________ >> [email protected] mailing list >> UNSUBSCRIBE and account-management -> >> http://lists.puredata.info/listinfo/pd-list >> >> >
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