It sounds like the Resonz UGen in supercollider is exactly what Julius Smith is talking about in that description of the two-pole filter.
But then there's the other supercollider filter UGens with "resonant" in the name, which seem more like what Martin was describing - RLPF (resonant low-pass filter) for example is a low-pass filter where you can adjust the resonance near the cutoff. I haven't played with this too much myself, but I'm guessing with the right Q value you could drive this to self-oscillation? Ultimately I think "resonant" is a general descriptive term for filters, that shouldn't be interpreted as a detail of implementation. On Tue, Jan 13, 2015 at 9:28 AM, Alexandre Torres Porres <[email protected]> wrote: > 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 >>> >>> >> >
_______________________________________________ [email protected] mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
