"*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 <ovaltinevor...@gmail.com>: > 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 <por...@gmail.com > > 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 <chakekat...@gmail.com>: >> >> 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 < >>> por...@gmail.com> 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 <ovaltinevor...@gmail.com>: >>>> >>>> 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 < >>>>> por...@gmail.com> wrote: >>>>> >>>>>> Hi, are bandpass and resonant filters the same? Or is there a >>>>>> difference between calling one a resonant and not a bandpass? >>>>>> >>>>>> thanks >>>>>> >>>>>> _______________________________________________ >>>>>> Pd-list@lists.iem.at mailing list >>>>>> UNSUBSCRIBE and account-management -> >>>>>> http://lists.puredata.info/listinfo/pd-list >>>>>> >>>>>> >>>>> >>>> >>>> _______________________________________________ >>>> Pd-list@lists.iem.at mailing list >>>> UNSUBSCRIBE and account-management -> >>>> http://lists.puredata.info/listinfo/pd-list >>>> >>>> >>> >> >
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