Re: [PD] vcf~ producing output without input for 0Hz cutoff?

2024-04-12 Thread Edwin van der Heide 
0 Hz is an infinite amount of octaves below 20 Hz (10 Hz, 5 Hz, 2.5 Hz, 1.25 Hz, …).A low pass filter “normally” has a slope of a certain amount dB per octave. However, a filter with a frequency of 0 Hz doesn’t  have a slope with a certain amount of dB/oct because an octave up or down from 0 Hz (by doubling or halving the frequency) is also 0 Hz. The filter simply can’t move ;-)Best!EdwinOn 12 Apr 2024, at 09:49, Christof Ressi  wrote:

  

  
  
Alex made a great point there!
It's that very reason why DAW plugins usually don't let you go
  down all the way to zero. (Typically, they stop at 20 Hz or
  something.) If your signal has components below that, you'd need a
  high pass filter.

On 12.04.2024 09:35, Alexandre Torres
  Porres wrote:


  
  oh sure, but that's more like a slew or glide and
you don't go down to zero anyway :)


and if you're filtering audio, you don't want to keep
  inaudible stuff. All I'm saying is that if you are soing this
  to fade to slience you need a DC filter
  
  
  
Em sex., 12 de abr. de 2024 às
  04:12, cyrille henry 
  escreveu:

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
  >
  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. >
  a écrit :
  > 
  >         * Antoine Rousseau >
  [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

Re: [PD] vcf~ producing output without input for 0Hz cutoff?

2024-04-12 Thread Christof Ressi 

Alex made a great point there!

It's that very reason why DAW plugins usually don't let you go down all 
the way to zero. (Typically, they stop at 20 Hz or something.) If your 
signal has components below that, you'd need a high pass filter.


On 12.04.2024 09:35, Alexandre Torres Porres wrote:
oh sure, but that's more like a slew or glide and you don't go down to 
zero anyway :)


and if you're filtering audio, you don't want to keep inaudible stuff. 
All I'm saying is that if you are soing this to fade to slience you 
need a DC filter


Em sex., 12 de abr. de 2024 às 04:12, cyrille henry  
escreveu:


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
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.
mailto:peterpar...@fastmail.com>> a écrit :
>
>         * Antoine Rousseau 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
>
>
>
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Re: [PD] vcf~ producing output without input for 0Hz cutoff?

2024-04-12 Thread Christof Ressi 
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 
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. > a écrit :


    * Antoine Rousseau > [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



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Re: [PD] vcf~ producing output without input for 0Hz cutoff?

2024-04-12 Thread Alexandre Torres Porres 
oh sure, but that's more like a slew or glide and you don't go down to zero
anyway :)

and if you're filtering audio, you don't want to keep inaudible stuff. All
I'm saying is that if you are soing this to fade to slience you need a DC
filter

Em sex., 12 de abr. de 2024 às 04:12, cyrille henry  escreveu:

> 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 > 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.  > 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
> >
> >
> >
> > ___
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Re: [PD] vcf~ producing output without input for 0Hz cutoff?

2024-04-12 Thread cyrille henry 

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 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. mailto:peterpar...@fastmail.com>> a écrit :

* Antoine Rousseau 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



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