Hi there, who can confirm that both [bp~] and [vcf~] are exactly the really same thingy? The code looks quite different...
Moreover, why the two outlets for vcf~? Help doesn't say anything.
Thanks
They're quite different. bp~ is the cheapest possible bandpass filter (as far as I know). vcf~ is a one-pole complex filter whose outputs are the real and imaginry parts. The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities.
It's possible to graph their frequency responses using the help patch "H10.measurement.pd' in 3.audio.examples.
cheers Miller
On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres wrote:
Hi there, who can confirm that both [bp~] and [vcf~] are exactly the really same thingy? The code looks quite different...
Moreover, why the two outlets for vcf~? Help doesn't say anything.
Thanks
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with just one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
They're quite different. bp~ is the cheapest possible bandpass filter (as far as I know). vcf~ is a one-pole complex filter whose outputs are the real and imaginry parts. The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities.
It's possible to graph their frequency responses using the help patch "H10.measurement.pd' in 3.audio.examples.
cheers Miller
On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres wrote:
Hi there, who can confirm that both [bp~] and [vcf~] are exactly the
really
same thingy? The code looks quite different...
Moreover, why the two outlets for vcf~? Help doesn't say anything.
Thanks
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management ->
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with just one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
They're quite different. bp~ is the cheapest possible bandpass filter (as far as I know). vcf~ is a one-pole complex filter whose outputs are the real and imaginry parts. The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities.
It's possible to graph their frequency responses using the help patch "H10.measurement.pd' in 3.audio.examples.
cheers Miller
On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres wrote:
Hi there, who can confirm that both [bp~] and [vcf~] are exactly the
really
same thingy? The code looks quite different...
Moreover, why the two outlets for vcf~? Help doesn't say anything.
Thanks
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management ->
Hi Miller, still trying to get my head around this. But anyway, one thing I have to note is that the source code of [vcf~] says it is a "two pole filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with just one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
They're quite different. bp~ is the cheapest possible bandpass filter (as far as I know). vcf~ is a one-pole complex filter whose outputs
are
the real and imaginry parts. The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities.
It's possible to graph their frequency responses using the help patch "H10.measurement.pd' in 3.audio.examples.
cheers Miller
On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres
wrote:
Hi there, who can confirm that both [bp~] and [vcf~] are exactly the
really
same thingy? The code looks quite different...
Moreover, why the two outlets for vcf~? Help doesn't say anything.
Thanks
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management ->
just chipping in with my 2 cents that it would be fantastic to get more documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres porres@gmail.com wrote:
Hi Miller, still trying to get my head around this. But anyway, one thing I have to note is that the source code of [vcf~] says it is a "two pole filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with just one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
They're quite different. bp~ is the cheapest possible bandpass filter (as far as I know). vcf~ is a one-pole complex filter whose outputs
are
the real and imaginry parts. The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities.
It's possible to graph their frequency responses using the help patch "H10.measurement.pd' in 3.audio.examples.
cheers Miller
On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres
wrote:
Hi there, who can confirm that both [bp~] and [vcf~] are exactly the
really
same thingy? The code looks quite different...
Moreover, why the two outlets for vcf~? Help doesn't say anything.
Thanks
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management ->
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities."
what sort of possibilities???
I wouldn't expect much about this. I guess it's like any other filters that can be combined in many ways.
Another thing I wanted to inquire is about bp~ having a frequency response that is not symmetric. The lower part of the spectrum has more energy. Could one consider it more of a "resonant low-pass filter", similar to [vcf~]'s second outlet?
By the way, while we're at it, I'd like to share something that may not be too important, but it's related. I was able to implement [cpole~] in [fexpr~]. Here it goes:
expr 1:
[fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); $x2 + ($x4 * $y1) + ($x3 * $y2)]
if we consider $x3 and $x4 as variables named, respectively, coefr (coeficient for the real part) and coefi (coeficient for the imaginary part), we then have:
expr 2:
*[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* *$x2** + (*coefi * $y1) + (coefr * $y2)]
Now, by checking the code of [vcf~] I was able to narrow down to its core formula, which is something like this
expr 3:
*ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; *(coefi * re2) + (coefr * im)*
the bolded letters in "expr 3" seem to match perfectly to "expr 2". The differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in expr 3).
That gets me closer to being able to implement [vcf~] with a [cpole~] I guess, but I find it weird that the imaginary output does not have the $x2 signal input to be added to the rest of the expression. I worry that actually prevents it from being successfully implemented with [cpole~]. Am I missing something?
Anyway, the thing is that I'm still really curious to learn wether vcf~ is a "two pole" filter or a "one complex pole" filter, and the reason behind it is because I believe we could make a biquad~ version of [vcf~] (at least for its real output). That's the bottom line.
cheers
2014-07-24 6:45 GMT-03:00 i go bananas hard.off@gmail.com:
just chipping in with my 2 cents that it would be fantastic to get more documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres <porres@gmail.com
wrote:
Hi Miller, still trying to get my head around this. But anyway, one thing I have to note is that the source code of [vcf~] says it is a "two pole filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with
just
one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
They're quite different. bp~ is the cheapest possible bandpass
filter
(as far as I know). vcf~ is a one-pole complex filter whose outputs
are
the real and imaginry parts. The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities.
It's possible to graph their frequency responses using the help patch "H10.measurement.pd' in 3.audio.examples.
cheers Miller
On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres
wrote:
Hi there, who can confirm that both [bp~] and [vcf~] are exactly
the
really
same thingy? The code looks quite different...
Moreover, why the two outlets for vcf~? Help doesn't say anything.
Thanks
Pd-list@iem.at mailing list UNSUBSCRIBE and account-management ->
Pd-list@lists.iem.at mailing list
UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
Yep, vcf~ isn't a 2-pole real filter but a 1-pole complex one (although its second outlet -- I think -- should be similar to a 2-pole real filter's output in theory, but in reality should be numerically more precise.)
I'll change the comment to something vaguer and more descriptive in the code..
Unless I'm badly mistaken, vcf~ is simply a cpole~ with extra stuff to compute the coefficient built in. There's no 'x2' because the input is taken to be real-valued.
cheers M
On Thu, Jul 24, 2014 at 01:18:28PM -0300, Alexandre Torres Porres wrote:
The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities."
what sort of possibilities???
I wouldn't expect much about this. I guess it's like any other filters that can be combined in many ways.
Another thing I wanted to inquire is about bp~ having a frequency response that is not symmetric. The lower part of the spectrum has more energy. Could one consider it more of a "resonant low-pass filter", similar to [vcf~]'s second outlet?
By the way, while we're at it, I'd like to share something that may not be too important, but it's related. I was able to implement [cpole~] in [fexpr~]. Here it goes:
expr 1:
[fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); $x2 + ($x4 * $y1) + ($x3 * $y2)]
if we consider $x3 and $x4 as variables named, respectively, coefr (coeficient for the real part) and coefi (coeficient for the imaginary part), we then have:
expr 2:
*[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* *$x2** + (*coefi * $y1) + (coefr * $y2)]
Now, by checking the code of [vcf~] I was able to narrow down to its core formula, which is something like this
expr 3:
*ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; *(coefi * re2) + (coefr * im)*
the bolded letters in "expr 3" seem to match perfectly to "expr 2". The differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in expr 3).
That gets me closer to being able to implement [vcf~] with a [cpole~] I guess, but I find it weird that the imaginary output does not have the $x2 signal input to be added to the rest of the expression. I worry that actually prevents it from being successfully implemented with [cpole~]. Am I missing something?
Anyway, the thing is that I'm still really curious to learn wether vcf~ is a "two pole" filter or a "one complex pole" filter, and the reason behind it is because I believe we could make a biquad~ version of [vcf~] (at least for its real output). That's the bottom line.
cheers
2014-07-24 6:45 GMT-03:00 i go bananas hard.off@gmail.com:
just chipping in with my 2 cents that it would be fantastic to get more documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres <porres@gmail.com
wrote:
Hi Miller, still trying to get my head around this. But anyway, one thing I have to note is that the source code of [vcf~] says it is a "two pole filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with
just
one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
They're quite different. bp~ is the cheapest possible bandpass
filter
(as far as I know). vcf~ is a one-pole complex filter whose outputs
are
the real and imaginry parts. The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities.
It's possible to graph their frequency responses using the help patch "H10.measurement.pd' in 3.audio.examples.
cheers Miller
On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres
wrote:
> Hi there, who can confirm that both [bp~] and [vcf~] are exactly
the
really > same thingy? The code looks quite different... > > Moreover, why the two outlets for vcf~? Help doesn't say anything. > > Thanks
> _______________________________________________ > Pd-list@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
yep, totally makes perfect sense to me now that it is a [cpole~].
I guess you can consider (ampcorrect * oneminusr) as a gain factor and multiply the input signal by this much before getting it to a [cpole~] with the same coefficients, and voilá... although getting all these coefficients to come up in a vanilla patch seems a lot of trouble...
But what I'm really and still dying to learn/figure out is whether a [cpole~] filter like [vcf~] could be obtained with [biquad~]. My intuition said: Yes. But after a few experiments I'm changing my mind... Can anyone just confirm me that?
What drove my intuition is the attached patch, which is a biquad~ filter made of raw filters I derived from mmb's work. If it made any sense is because it is implemented with [cpole~] and [czero~] objects, so it seemed that a set of biquad coefficients could result in just a couple of coefficients for one [cpole~]. But then, by checking it out and trying to do it, it doens't seem possible to get a coordinate pair for a [cpole~] with biquad coefficients... hmmm, bummer.
Any thoughts?
thanks
2014-07-24 13:33 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep, vcf~ isn't a 2-pole real filter but a 1-pole complex one (although its second outlet -- I think -- should be similar to a 2-pole real filter's output in theory, but in reality should be numerically more precise.)
I'll change the comment to something vaguer and more descriptive in the code..
Unless I'm badly mistaken, vcf~ is simply a cpole~ with extra stuff to compute the coefficient built in. There's no 'x2' because the input is taken to be real-valued.
cheers M
On Thu, Jul 24, 2014 at 01:18:28PM -0300, Alexandre Torres Porres wrote:
The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities."
what sort of possibilities???
I wouldn't expect much about this. I guess it's like any other filters
that
can be combined in many ways.
Another thing I wanted to inquire is about bp~ having a frequency
response
that is not symmetric. The lower part of the spectrum has more energy. Could one consider it more of a "resonant low-pass filter", similar to [vcf~]'s second outlet?
By the way, while we're at it, I'd like to share something that may not
be
too important, but it's related. I was able to implement [cpole~] in [fexpr~]. Here it goes:
expr 1:
[fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); $x2 + ($x4 * $y1) + ($x3 * $y2)]
if we consider $x3 and $x4 as variables named, respectively, coefr (coeficient for the real part) and coefi (coeficient for the imaginary part), we then have:
expr 2:
*[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* *$x2** + (*coefi * $y1) + (coefr * $y2)]
Now, by checking the code of [vcf~] I was able to narrow down to its core formula, which is something like this
expr 3:
*ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; *(coefi * re2) + (coefr * im)*
the bolded letters in "expr 3" seem to match perfectly to "expr 2". The differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in
expr
3).
That gets me closer to being able to implement [vcf~] with a [cpole~] I guess, but I find it weird that the imaginary output does not have the
$x2
signal input to be added to the rest of the expression. I worry that actually prevents it from being successfully implemented with [cpole~].
Am
I missing something?
Anyway, the thing is that I'm still really curious to learn wether vcf~
is
a "two pole" filter or a "one complex pole" filter, and the reason behind it is because I believe we could make a biquad~ version of [vcf~] (at
least
for its real output). That's the bottom line.
cheers
2014-07-24 6:45 GMT-03:00 i go bananas hard.off@gmail.com:
just chipping in with my 2 cents that it would be fantastic to get more documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres <
porres@gmail.com
wrote:
Hi Miller, still trying to get my head around this. But anyway, one
thing
I have to note is that the source code of [vcf~] says it is a "two
pole
filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres
wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with
just
one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
> They're quite different. bp~ is the cheapest possible bandpass
filter
> (as far as I know). vcf~ is a one-pole complex filter whose
outputs
are
> the real and imaginry parts. The real part may be used as a
resonant
> bandpass filter and the imaginary as a resonant low-pass filter,
but
> they can be combined to make other possibilities. > > It's possible to graph their frequency responses using the help
patch
> "H10.measurement.pd' in 3.audio.examples. > > cheers > Miller > > On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres
wrote:
> > Hi there, who can confirm that both [bp~] and [vcf~] are
exactly
the
> really > > same thingy? The code looks quite different... > > > > Moreover, why the two outlets for vcf~? Help doesn't say
anything.
> > > > Thanks > > > _______________________________________________ > > Pd-list@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
whether a [cpole~] filter like [vcf~] could be obtained with [biquad~].
I meant at least the real output of [vcf~]
2014-07-24 14:28 GMT-03:00 Alexandre Torres Porres porres@gmail.com:
yep, totally makes perfect sense to me now that it is a [cpole~].
I guess you can consider (ampcorrect * oneminusr) as a gain factor and multiply the input signal by this much before getting it to a [cpole~] with the same coefficients, and voilá... although getting all these coefficients to come up in a vanilla patch seems a lot of trouble...
But what I'm really and still dying to learn/figure out is whether a [cpole~] filter like [vcf~] could be obtained with [biquad~]. My intuition said: Yes. But after a few experiments I'm changing my mind... Can anyone just confirm me that?
What drove my intuition is the attached patch, which is a biquad~ filter made of raw filters I derived from mmb's work. If it made any sense is because it is implemented with [cpole~] and [czero~] objects, so it seemed that a set of biquad coefficients could result in just a couple of coefficients for one [cpole~]. But then, by checking it out and trying to do it, it doens't seem possible to get a coordinate pair for a [cpole~] with biquad coefficients... hmmm, bummer.
Any thoughts?
thanks
2014-07-24 13:33 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep, vcf~ isn't a 2-pole real filter but a 1-pole complex one (although
its second outlet -- I think -- should be similar to a 2-pole real filter's output in theory, but in reality should be numerically more precise.)
I'll change the comment to something vaguer and more descriptive in the code..
Unless I'm badly mistaken, vcf~ is simply a cpole~ with extra stuff to compute the coefficient built in. There's no 'x2' because the input is taken to be real-valued.
cheers M
On Thu, Jul 24, 2014 at 01:18:28PM -0300, Alexandre Torres Porres wrote:
The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities."
what sort of possibilities???
I wouldn't expect much about this. I guess it's like any other filters
that
can be combined in many ways.
Another thing I wanted to inquire is about bp~ having a frequency
response
that is not symmetric. The lower part of the spectrum has more energy. Could one consider it more of a "resonant low-pass filter", similar to [vcf~]'s second outlet?
By the way, while we're at it, I'd like to share something that may not
be
too important, but it's related. I was able to implement [cpole~] in [fexpr~]. Here it goes:
expr 1:
[fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); $x2 + ($x4 * $y1) + ($x3 * $y2)]
if we consider $x3 and $x4 as variables named, respectively, coefr (coeficient for the real part) and coefi (coeficient for the imaginary part), we then have:
expr 2:
*[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* *$x2** + (*coefi * $y1) + (coefr * $y2)]
Now, by checking the code of [vcf~] I was able to narrow down to its
core
formula, which is something like this
expr 3:
*ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; *(coefi * re2) + (coefr * im)*
the bolded letters in "expr 3" seem to match perfectly to "expr 2". The differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in
expr
3).
That gets me closer to being able to implement [vcf~] with a [cpole~] I guess, but I find it weird that the imaginary output does not have the
$x2
signal input to be added to the rest of the expression. I worry that actually prevents it from being successfully implemented with [cpole~].
Am
I missing something?
Anyway, the thing is that I'm still really curious to learn wether vcf~
is
a "two pole" filter or a "one complex pole" filter, and the reason
behind
it is because I believe we could make a biquad~ version of [vcf~] (at
least
for its real output). That's the bottom line.
cheers
2014-07-24 6:45 GMT-03:00 i go bananas hard.off@gmail.com:
just chipping in with my 2 cents that it would be fantastic to get
more
documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres <
porres@gmail.com
wrote:
Hi Miller, still trying to get my head around this. But anyway, one
thing
I have to note is that the source code of [vcf~] says it is a "two
pole
filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres
wrote:
> that's great to know, thanks! > > Let me just see if I get a bit of the theory. Can I get [vcf~]
with
just > one [cpole~] object and the right coeficients? > > Cheers > > > 2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu: > > > They're quite different. bp~ is the cheapest possible bandpass filter > > (as far as I know). vcf~ is a one-pole complex filter whose
outputs
are > > the real and imaginry parts. The real part may be used as a
resonant
> > bandpass filter and the imaginary as a resonant low-pass
filter, but
> > they can be combined to make other possibilities. > > > > It's possible to graph their frequency responses using the help
patch
> > "H10.measurement.pd' in 3.audio.examples. > > > > cheers > > Miller > > > > On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres
Porres
wrote: > > > Hi there, who can confirm that both [bp~] and [vcf~] are
exactly
the > > really > > > same thingy? The code looks quite different... > > > > > > Moreover, why the two outlets for vcf~? Help doesn't say
anything.
> > > > > > Thanks > > > > > _______________________________________________ > > > Pd-list@iem.at mailing list > > > UNSUBSCRIBE and account-management -> > > http://lists.puredata.info/listinfo/pd-list > > > >
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Since there's been quite some discussion on this subject, I'll bump in to share eight externals I wrote, based on Mike Moser-Booth's (mmb) [flitercoeff.mmb~] and [biquad.mmb~] abstractions. The objects are: [lowPass~], [bandPass~], [highPass~], [allPass~], [resonant~], [lowShelf~], [peakNotch~] and [highShelf~]. They all have only signal inlets to avoid clicks when changing parameters. You can get them here http://drymonitis.me/code/ look for the "Various filters" link. The .zip file contains binaries for OS X and Linux, help patches (dunno if they are very helpful), source code, Pd's generic Makefile and a README. Comments are welcome.
On Thu, Jul 24, 2014 at 8:40 PM, Alexandre Torres Porres porres@gmail.com wrote:
whether a [cpole~] filter like [vcf~] could be obtained with [biquad~].
I meant at least the real output of [vcf~]
2014-07-24 14:28 GMT-03:00 Alexandre Torres Porres porres@gmail.com:
yep, totally makes perfect sense to me now that it is a [cpole~].
I guess you can consider (ampcorrect * oneminusr) as a gain factor and multiply the input signal by this much before getting it to a [cpole~] with the same coefficients, and voilá... although getting all these coefficients to come up in a vanilla patch seems a lot of trouble...
But what I'm really and still dying to learn/figure out is whether a [cpole~] filter like [vcf~] could be obtained with [biquad~]. My intuition said: Yes. But after a few experiments I'm changing my mind... Can anyone just confirm me that?
What drove my intuition is the attached patch, which is a biquad~ filter made of raw filters I derived from mmb's work. If it made any sense is because it is implemented with [cpole~] and [czero~] objects, so it seemed that a set of biquad coefficients could result in just a couple of coefficients for one [cpole~]. But then, by checking it out and trying to do it, it doens't seem possible to get a coordinate pair for a [cpole~] with biquad coefficients... hmmm, bummer.
Any thoughts?
thanks
2014-07-24 13:33 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep, vcf~ isn't a 2-pole real filter but a 1-pole complex one (although
its second outlet -- I think -- should be similar to a 2-pole real filter's output in theory, but in reality should be numerically more precise.)
I'll change the comment to something vaguer and more descriptive in the code..
Unless I'm badly mistaken, vcf~ is simply a cpole~ with extra stuff to compute the coefficient built in. There's no 'x2' because the input is taken to be real-valued.
cheers M
On Thu, Jul 24, 2014 at 01:18:28PM -0300, Alexandre Torres Porres wrote:
The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities."
what sort of possibilities???
I wouldn't expect much about this. I guess it's like any other filters
that
can be combined in many ways.
Another thing I wanted to inquire is about bp~ having a frequency
response
that is not symmetric. The lower part of the spectrum has more energy. Could one consider it more of a "resonant low-pass filter", similar to [vcf~]'s second outlet?
By the way, while we're at it, I'd like to share something that may
not be
too important, but it's related. I was able to implement [cpole~] in [fexpr~]. Here it goes:
expr 1:
[fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); $x2 + ($x4 * $y1) + ($x3 * $y2)]
if we consider $x3 and $x4 as variables named, respectively, coefr (coeficient for the real part) and coefi (coeficient for the imaginary part), we then have:
expr 2:
*[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* *$x2** + (*coefi * $y1) + (coefr * $y2)]
Now, by checking the code of [vcf~] I was able to narrow down to its
core
formula, which is something like this
expr 3:
*ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; *(coefi * re2) + (coefr * im)*
the bolded letters in "expr 3" seem to match perfectly to "expr 2". The differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in
expr
3).
That gets me closer to being able to implement [vcf~] with a [cpole~] I guess, but I find it weird that the imaginary output does not have the
$x2
signal input to be added to the rest of the expression. I worry that actually prevents it from being successfully implemented with
[cpole~]. Am
I missing something?
Anyway, the thing is that I'm still really curious to learn wether
vcf~ is
a "two pole" filter or a "one complex pole" filter, and the reason
behind
it is because I believe we could make a biquad~ version of [vcf~] (at
least
for its real output). That's the bottom line.
cheers
2014-07-24 6:45 GMT-03:00 i go bananas hard.off@gmail.com:
just chipping in with my 2 cents that it would be fantastic to get
more
documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres <
porres@gmail.com
wrote:
Hi Miller, still trying to get my head around this. But anyway, one
thing
I have to note is that the source code of [vcf~] says it is a "two
pole
filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~. > > cheers > M > > On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres
wrote:
> > that's great to know, thanks! > > > > Let me just see if I get a bit of the theory. Can I get [vcf~]
with
> just > > one [cpole~] object and the right coeficients? > > > > Cheers > > > > > > 2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu: > > > > > They're quite different. bp~ is the cheapest possible bandpass > filter > > > (as far as I know). vcf~ is a one-pole complex filter whose
outputs
> are > > > the real and imaginry parts. The real part may be used as a
resonant
> > > bandpass filter and the imaginary as a resonant low-pass
filter, but
> > > they can be combined to make other possibilities. > > > > > > It's possible to graph their frequency responses using the
help patch
> > > "H10.measurement.pd' in 3.audio.examples. > > > > > > cheers > > > Miller > > > > > > On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres
Porres
> wrote: > > > > Hi there, who can confirm that both [bp~] and [vcf~] are
exactly
> the > > > really > > > > same thingy? The code looks quite different... > > > > > > > > Moreover, why the two outlets for vcf~? Help doesn't say
anything.
> > > > > > > > Thanks > > > > > > > _______________________________________________ > > > > Pd-list@iem.at mailing list > > > > UNSUBSCRIBE and account-management -> > > > http://lists.puredata.info/listinfo/pd-list > > > > > > >
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vcf~ isn't a 2-pole real filter but a 1-pole complex one
kinda relative to this, since biquad~ can be emulated with 2 complex poles
- 2 complex zeros, is it more accurate to say biquad is a
2-complex_pole-2-complex_zero-filter???
In its description it says it is a 2-pole-2-zero-filter...
cheers
2014-07-24 13:33 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep, vcf~ isn't a 2-pole real filter but a 1-pole complex one (although its second outlet -- I think -- should be similar to a 2-pole real filter's output in theory, but in reality should be numerically more precise.)
I'll change the comment to something vaguer and more descriptive in the code..
Unless I'm badly mistaken, vcf~ is simply a cpole~ with extra stuff to compute the coefficient built in. There's no 'x2' because the input is taken to be real-valued.
cheers M
On Thu, Jul 24, 2014 at 01:18:28PM -0300, Alexandre Torres Porres wrote:
The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities."
what sort of possibilities???
I wouldn't expect much about this. I guess it's like any other filters
that
can be combined in many ways.
Another thing I wanted to inquire is about bp~ having a frequency
response
that is not symmetric. The lower part of the spectrum has more energy. Could one consider it more of a "resonant low-pass filter", similar to [vcf~]'s second outlet?
By the way, while we're at it, I'd like to share something that may not
be
too important, but it's related. I was able to implement [cpole~] in [fexpr~]. Here it goes:
expr 1:
[fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); $x2 + ($x4 * $y1) + ($x3 * $y2)]
if we consider $x3 and $x4 as variables named, respectively, coefr (coeficient for the real part) and coefi (coeficient for the imaginary part), we then have:
expr 2:
*[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* *$x2** + (*coefi * $y1) + (coefr * $y2)]
Now, by checking the code of [vcf~] I was able to narrow down to its core formula, which is something like this
expr 3:
*ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; *(coefi * re2) + (coefr * im)*
the bolded letters in "expr 3" seem to match perfectly to "expr 2". The differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in
expr
3).
That gets me closer to being able to implement [vcf~] with a [cpole~] I guess, but I find it weird that the imaginary output does not have the
$x2
signal input to be added to the rest of the expression. I worry that actually prevents it from being successfully implemented with [cpole~].
Am
I missing something?
Anyway, the thing is that I'm still really curious to learn wether vcf~
is
a "two pole" filter or a "one complex pole" filter, and the reason behind it is because I believe we could make a biquad~ version of [vcf~] (at
least
for its real output). That's the bottom line.
cheers
2014-07-24 6:45 GMT-03:00 i go bananas hard.off@gmail.com:
just chipping in with my 2 cents that it would be fantastic to get more documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres <
porres@gmail.com
wrote:
Hi Miller, still trying to get my head around this. But anyway, one
thing
I have to note is that the source code of [vcf~] says it is a "two
pole
filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres
wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with
just
one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
> They're quite different. bp~ is the cheapest possible bandpass
filter
> (as far as I know). vcf~ is a one-pole complex filter whose
outputs
are
> the real and imaginry parts. The real part may be used as a
resonant
> bandpass filter and the imaginary as a resonant low-pass filter,
but
> they can be combined to make other possibilities. > > It's possible to graph their frequency responses using the help
patch
> "H10.measurement.pd' in 3.audio.examples. > > cheers > Miller > > On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres
wrote:
> > Hi there, who can confirm that both [bp~] and [vcf~] are
exactly
the
> really > > same thingy? The code looks quite different... > > > > Moreover, why the two outlets for vcf~? Help doesn't say
anything.
> > > > Thanks > > > _______________________________________________ > > Pd-list@iem.at mailing list > > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > >
Pd-list@lists.iem.at mailing list
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On 07/24/2014 10:14 PM, Alexandre Torres Porres wrote:
vcf~ isn't a 2-pole real filter but a 1-pole complex one
kinda relative to this, since biquad~ can be emulated with 2 complex poles
- 2 complex zeros
it can not only be emulated, it can be implemented with a complex 2-pole/2-zero filter.
, is it more accurate to say biquad is a 2-complex_pole-2-complex_zero-filter???
no. it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
real values are a subset of complex values (with the imaginary part set to 0).
In its description it says it is a 2-pole-2-zero-filter...
which is true.
gfmasdr IOhannes
it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
but why, if the poles and zeros can have complex values?
2014-07-25 8:18 GMT-03:00 IOhannes m zmölnig zmoelnig@iem.at:
On 07/24/2014 10:14 PM, Alexandre Torres Porres wrote:
vcf~ isn't a 2-pole real filter but a 1-pole complex one
kinda relative to this, since biquad~ can be emulated with 2 complex
poles
- 2 complex zeros
it can not only be emulated, it can be implemented with a complex 2-pole/2-zero filter.
, is it more accurate to say biquad is a 2-complex_pole-2-complex_zero-filter???
no. it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
real values are a subset of complex values (with the imaginary part set to 0).
In its description it says it is a 2-pole-2-zero-filter...
which is true.
gfmasdr IOhannes
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On 25/07/14 14:36, Alexandre Torres Porres wrote:
it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
but why, if the poles and zeros can have complex values?
If the poles (zeros) occur in as a complex conjugate pair (with identical real parts and opposite imaginary parts), or both poles (zeros) are real, then the filter will have real output for real input. Having only real coeffecients for biquad forces the poles (zeros) to take this form.
Claude
Having only real coeffecients for biquad forces the poles (zeros) to take
this form.
yeah, that makes sense. The tricky part seems to be how a complex conjugate pair does that too. Is it because you'd add them up and then the imaginary part becomes zero? That's what I can think of...
2014-07-25 10:49 GMT-03:00 Claude Heiland-Allen claude@mathr.co.uk:
On 25/07/14 14:36, Alexandre Torres Porres wrote:
it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
but why, if the poles and zeros can have complex values?
If the poles (zeros) occur in as a complex conjugate pair (with identical real parts and opposite imaginary parts), or both poles (zeros) are real, then the filter will have real output for real input. Having only real coeffecients for biquad forces the poles (zeros) to take this form.
Claude
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On 07/25/2014 03:36 PM, Alexandre Torres Porres wrote:
it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
but why, if the poles and zeros can have complex values?
can they? afaict, [biquad~] only ever has real-valued coefficients and states.
df,ase IOhannes
On 25/07/14 16:06, IOhannes m zmölnig wrote:
On 07/25/2014 03:36 PM, Alexandre Torres Porres wrote:
it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
but why, if the poles and zeros can have complex values?
can they?
Yes, but they occur in conjugate pairs, as the transfer function has real coefficients:
a s^2 + b s + c (s - z1) (s - z2)
H(s) = --------------- = k ----------------- e s^2 + f s + g (s - p1) (s - p2)
-b +/- sqrt(b^2 - 4 a c)
z1,z2 = ------------------------ 2 a
-f +/- sqrt(f^2 - 4 e g)
p1,p2 = ------------------------ 2 e
inside the sqrt is positive -> two real roots inside the sqrt is negative -> complex conjugate pair
The imaginary parts of the complex conjugate "cancel out" to the quadratic polynomial with all-real coefficients.
afaict, [biquad~] only ever has real-valued coefficients and states.
sure, just different representations of the same thing
Claude
"its second outlet -- I think -- should be similar to a 2-pole real filter's output in theory, but in reality should be numerically more precise."
I guess relates to what I was asking if [bp~] could be considered more of a "resonant low-pass filter" instead of a bandpass, similar to [vcf~]'s second outlet. I asked it because the frequency response is similarly shaped, and now you mention that this second outlet is similar to a 2-pole real filter's output... well, [bp~] is said to be a 2 pole real filter, so there it goes... huh?
cheers
2014-07-24 13:33 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep, vcf~ isn't a 2-pole real filter but a 1-pole complex one (although its second outlet -- I think -- should be similar to a 2-pole real filter's output in theory, but in reality should be numerically more precise.)
I'll change the comment to something vaguer and more descriptive in the code..
Unless I'm badly mistaken, vcf~ is simply a cpole~ with extra stuff to compute the coefficient built in. There's no 'x2' because the input is taken to be real-valued.
cheers M
On Thu, Jul 24, 2014 at 01:18:28PM -0300, Alexandre Torres Porres wrote:
The real part may be used as a resonant bandpass filter and the imaginary as a resonant low-pass filter, but they can be combined to make other possibilities."
what sort of possibilities???
I wouldn't expect much about this. I guess it's like any other filters
that
can be combined in many ways.
Another thing I wanted to inquire is about bp~ having a frequency
response
that is not symmetric. The lower part of the spectrum has more energy. Could one consider it more of a "resonant low-pass filter", similar to [vcf~]'s second outlet?
By the way, while we're at it, I'd like to share something that may not
be
too important, but it's related. I was able to implement [cpole~] in [fexpr~]. Here it goes:
expr 1:
[fexpr~ $x1 + ($x3 * $y1) - ($x4 * $y2); $x2 + ($x4 * $y1) + ($x3 * $y2)]
if we consider $x3 and $x4 as variables named, respectively, coefr (coeficient for the real part) and coefi (coeficient for the imaginary part), we then have:
expr 2:
*[fexpr~ $x1 + (coefr * $y1) - (coefi * $y2);* *$x2** + (*coefi * $y1) + (coefr * $y2)]
Now, by checking the code of [vcf~] I was able to narrow down to its core formula, which is something like this
expr 3:
*ampcorrect * oneminusr* * *f1 + (coefr * re2) - (coefi * im)*; *(coefi * re2) + (coefr * im)*
the bolded letters in "expr 3" seem to match perfectly to "expr 2". The differences are underlined ($x2 in expr 2 and ampcorrect/oneminusr in
expr
3).
That gets me closer to being able to implement [vcf~] with a [cpole~] I guess, but I find it weird that the imaginary output does not have the
$x2
signal input to be added to the rest of the expression. I worry that actually prevents it from being successfully implemented with [cpole~].
Am
I missing something?
Anyway, the thing is that I'm still really curious to learn wether vcf~
is
a "two pole" filter or a "one complex pole" filter, and the reason behind it is because I believe we could make a biquad~ version of [vcf~] (at
least
for its real output). That's the bottom line.
cheers
2014-07-24 6:45 GMT-03:00 i go bananas hard.off@gmail.com:
just chipping in with my 2 cents that it would be fantastic to get more documented info on all this.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
On Thu, Jul 24, 2014 at 5:07 PM, Alexandre Torres Porres <
porres@gmail.com
wrote:
Hi Miller, still trying to get my head around this. But anyway, one
thing
I have to note is that the source code of [vcf~] says it is a "two
pole
filter", not a "one complex pole" filter.
Should that description be changed? If not, why?
thanks
2014-04-12 14:13 GMT-03:00 Miller Puckette msp@ucsd.edu:
Yep - vcf~ is essentially a wrapper for cpole~.
cheers M
On Sat, Apr 12, 2014 at 02:10:19PM -0300, Alexandre Torres Porres
wrote:
that's great to know, thanks!
Let me just see if I get a bit of the theory. Can I get [vcf~] with
just
one [cpole~] object and the right coeficients?
Cheers
2014-04-12 13:36 GMT-03:00 Miller Puckette msp@ucsd.edu:
> They're quite different. bp~ is the cheapest possible bandpass
filter
> (as far as I know). vcf~ is a one-pole complex filter whose
outputs
are
> the real and imaginry parts. The real part may be used as a
resonant
> bandpass filter and the imaginary as a resonant low-pass filter,
but
> they can be combined to make other possibilities. > > It's possible to graph their frequency responses using the help
patch
> "H10.measurement.pd' in 3.audio.examples. > > cheers > Miller > > On Sat, Apr 12, 2014 at 04:28:11AM -0300, Alexandre Torres Porres
wrote:
> > Hi there, who can confirm that both [bp~] and [vcf~] are
exactly
the
> really > > same thingy? The code looks quite different... > > > > Moreover, why the two outlets for vcf~? Help doesn't say
anything.
> > > > Thanks > > > _______________________________________________ > > Pd-list@iem.at mailing list > > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > >
Pd-list@lists.iem.at mailing list
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On 24/07/14 19:45, i go bananas wrote:
just chipping in with my 2 cents that it would be fantastic to get more documented info on all this.
it is a big topic ... Miller has a chapter "Filters" in Theory and Techniques of Electronic Music if you want it shown via Pd, in his words, otherwise there are lots of other texts out there.
especially curious about: "but they can be combined to make other possibilities."
what sort of possibilities???
-
Alexandre Torres Porres -
Alexandros Drymonitis -
Claude Heiland-Allen -
i go bananas -
IOhannes m zmölnig -
Miller Puckette -
Simon Wise