This bit of the wikipedia article on resonance about "Q" ( http://en.wikipedia.org/wiki/Resonance#Q_factor ) mentions a lot of what we read about "Ringing Filter", and how a higher Q will make it "ring" longer... this is what you get from that bandpass in the EQ Cookbook that says it has "constant skirt gain, peak gain = Q" - or what I'm assuming to be a "resonant filter by excellence" or whatever...
cheers 2015-01-13 13:38 GMT-02:00 Alexandre Torres Porres <[email protected]>: > "*Ultimately I think "resonant" is a general descriptive term for > filters, that shouldn't be interpreted as a detail of implementation.*" > > I guess you have a point there, and I was also driving to this conclusion. > > "*It sounds like the Resonz UGen in supercollider is exactly what Julius > Smith is talking about in that description of the two-pole filter.*" > > Actually, the Resonz UGen is a Two Pole / Two Zero filter, which is very > more closely related to [cyclone/reson~]. > > A Two-Pole only filter (no zeros) like the one Julius is describing is > actually what the [bp~] object is! > > "*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.* " > > Yep, and this is also much like the [cyclone/lores~] object in Pd. Check > that patch I sent for more detailed info on these filters. > > I've always assumed that a filter, in order to be called a "resonant > filter" or a "resonator" - being it a low pass, a high pass or a band pass > -, needed to boost/add gain to a particular cutoff frequency (in the case > of lowpass and highpas - which is the case for [lores~] or RLPF) or add > gain to some center frequency (in the case of a bandpass) - which is also > called "resonant frequency". > > The quote from Julius in that link - where he says "*A resonator is a > recursive filter that boosts signal amplitude at a particular frequency*" > - is in line with my assumption. > > But the concept of resonance in physics, in its utmost purity according to > wikipedia, is that it "is the tendency of a system to oscillate with > greater amplitude at some frequencies than at others". Meaning that it > doesn't really have to add gain to something, but only favor a frequency > amongst others... In this context, a bandpass - in general - is a > "resonator"... > > But it'd be cool if I could find a definitive word about this in the > filter literature! > > Cheers > > 2015-01-13 13:16 GMT-02:00 Brian Fay <[email protected]>: > > 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 >>>>> >>>>> >>>> >>> >> >
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