Em sáb., 13 de abr. de 2024 às 06:30, Peter P. <peterpar...@fastmail.com> escreveu:
> Looking at [vcf~]'s help patch closer, I read that the filter's real and > complex outputs may be combined to allow for other filtering possibilies > than band-pass and low-pass. Does anyone have a quick example of such a > combination? I don't, and this information was there before I revised all help files. I suspect Miller wrote this, but I can't see how this is helpful or insightful information. This would not be something particular to [vcf~], any filter can be cascaded or combined in parallel, and I guess this is beter suited for the raw filters, that can be used and combined to more properly design filters. I would vote for just suppressing this information, unless someone convinces me there's a good point and example. > I reckon that I make a highpass filter by subtracting the > lowpass-filtered signal from the same unfiltered signal? > Well, this is not MAX, we do have [hip~] :) > > Thanks again to everyone, > Peter > > * Christof Ressi <i...@christofressi.com> [2024-04-12 09:36]: > > Just expand on Antoine's post, let's look at the formula of Pd's 1-pole > > lowpass filter: > > > > k = freq * 2pi / sr > > > > y[i] = x[i] * k + y[i-1] * (1 - k) > > > > For freq=0 this becomes: > > > > y[i] = y[i-1] > > > > As you can see, this would just repeat the previous output infinitely, > > ignoring the input altogether. There is no decay to zero! > > > > The same reasoning applies to bandpass filters such as [vcf~]. > > > > Christof > > > > On 12.04.2024 09:10, cyrille henry wrote: > > > I don't think it's weird for a lowpass filter to go under 20Hz. They > are > > > not restricted to audio signals. > > > I use them a lot to smooth control signals, or to replace line~. > > > (I really hate line~ to control sound amplitude or preset transition, > > > it's way too robotic) > > > > > > cheers > > > c > > > > > > Le 12/04/2024 à 08:01, Alexandre Torres Porres a écrit : > > > > and you got a strong DC component over there :) > > > > > > > > anyway, it also seems weird to have a lowpass or a bandpass going as > > > > low as in the 20hz range. If you wanna do it just so it fades out to > > > > silence, you need a DC filter, something like a [hip~ 5] object, so > > > > when the lowpass, bandpass gets there, then you have nothing. > > > > > > > > cheers > > > > > > > > Em qui., 11 de abr. de 2024 às 15:40, Antoine Rousseau > > > > <anto...@metalu.net <mailto:anto...@metalu.net>> escreveu: > > > > > > > > Well, let's simplify a bit, forget all the filter complexity (Q, > > > > slope, definition of the cutoff frequency...). > > > > > > > > Let's just say that the output of a lowpass filter cannot move > > > > faster than the cutoff frequency: a 1Hz filter output cannot move > > > > faster than 1Hz (so it can't go back and forth in less than a second > > > > or so), a 1kHz can't go back and forth in less than about 1ms, etc. > > > > The output of a 0Hz filter can't move... at all. When you set the > > > > cutoff to 0Hz, the output freezes to its current value. It won't > > > > magically decay to 0. > > > > > > > > Hey, if you set the framerate of a movie to 0 frame/second, it > > > > will just stop, and will show the same image forever; it won't fade > > > > to black! > > > > > > > > Antoine > > > > > > > > > > > > > > > > Le jeu. 11 avr. 2024 à 14:08, Peter P. <peterpar...@fastmail.com > > > > <mailto:peterpar...@fastmail.com>> a écrit : > > > > > > > > * Antoine Rousseau <anto...@metalu.net > > > > <mailto:anto...@metalu.net>> [2024-04-11 13:40]: > > > > > That doesn't seem incorrect to me; after all, a lowpass > > > > filter at 0Hz > > > > > implies that its output is constant (any change would > > > > involve frequencies > > > > > > 0Hz). > > > > > > > > Thanks Antoine, > > > > > > > > Why does a lowpass filter, that has a cutoff frequency of > > > > 0Hz imply that > > > > it's output is constant? > > > > > > > > I will describe the problem again hoping that I will > > > > understand it > > > > better myseld: > > > > I have an oscillating input signal that has some DC offset > > > > (unipolar > > > > sawtooth from phasor~). I fade this signal's amplitude to > > > > -inf dB using > > > > [line~]. > > > > > > > > I also fade down the filter cutoff (defined as the -3dB > > > > point of the > > > > filter curve) from 400Hz to 0Hz. The filter will then > > > > continue to produce an > > > > non-decaying output. > > > > > > > > If I fade down the filter cutoff down to only 1Hz, it's > > > > output will decay (somehow > > > > counterintuitively to me). This is the part I don't get. > > > > > > > > I understand that vcf~ is a resonant filter, and it can have > > > > a gain > > > > greater 1 around the cutoff frequency, especially for high Q > > > > values. The > > > > above behavior can also be observed for Q=1. > > > > > > > > Thanks for all hints! > > > > Peter > > > > > > > > > > > > > > > > _______________________________________________ > > > > Pd-list@lists.iem.at <mailto:Pd-list@lists.iem.at> mailing > list > > > > UNSUBSCRIBE and account-management -> > > > > https://lists.puredata.info/listinfo/pd-list > > > > <https://lists.puredata.info/listinfo/pd-list> > > > > > > > > _______________________________________________ > > > > Pd-list@lists.iem.at <mailto:Pd-list@lists.iem.at> mailing list > > > > UNSUBSCRIBE and account-management -> > > > > https://lists.puredata.info/listinfo/pd-list > > > > <https://lists.puredata.info/listinfo/pd-list> > > > > > > > > > > > > _______________________________________________ > > > > Pd-list@lists.iem.at mailing list > > > > UNSUBSCRIBE and account-management -> > > > > https://lists.puredata.info/listinfo/pd-list > > > > > > > > > > > > _______________________________________________ > > > Pd-list@lists.iem.at mailing list > > > UNSUBSCRIBE and account-management -> > > > https://lists.puredata.info/listinfo/pd-list > > > > > > > > _______________________________________________ > > Pd-list@lists.iem.at mailing list > > UNSUBSCRIBE and account-management -> > https://lists.puredata.info/listinfo/pd-list > > > > _______________________________________________ > Pd-list@lists.iem.at mailing list > UNSUBSCRIBE and account-management -> > https://lists.puredata.info/listinfo/pd-list >
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