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> 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> a > écrit : > >> * Antoine Rousseau <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 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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