What's the best or "correct" way to add resonance to a [vcf~]?
- Should the feedback be delayed?
- Should the feedback be inverted?
- Should the feedback be from the outlet I'm using?
- Or should the feedback always come from the BP or HiPass side?
Thanks! BH
-- William Huston: WilliamAHuston@gmail.com Binghamton NY
*Public Service Mapping / Videography / Research* Blog http://WilliamAHuston.blogspot.com -- Facebook http://facebook.com/billhuston -- Twitter http://twitter.com/WilliamAHuston-- Youtube https://www.youtube.com/channel/UCGijK1amWOLglT3YeTyEBNQ?sub_congfirmation=1 Document collections: VirtualPipelines http://TinyURL.com/VirtualPipelines -- BHDCSDimockArchive http://bit.ly/BHDCSDimockArchive Please support my work: TinyURL.com/DonateToBillHuston
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics... If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (http://www.birthofasynth.com/Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf) you will see that the signal path from input to output goes through 5 inversion stages before being fed back into the input to generate resonance. Therefore it is inverted.
Since most (resonant) filters consist of an even number of stages (and therefore an even number of poles and/or zeroes) you should probably invert the feedback. With an odd number you should probably not invert feedback. My guess is that vcf~ implements an even-number (probably 4-pole) resonant filter, a la Moog. You can also try mvcf~ from my library (ekext - http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about.
This might seem counter-intuitive, but the image below shows how this works with regards to vcf~ - the output of vcf~ is NOT inverted, whereas the output of an analog VCF should be.
Odd-number staged filters are very rare in the analog world, and most (i.e. 18dB per octave) were created to implement the (mythical 3-pole topology) filter of the Roland TB303. However, according to the schematics of the TB303 it is a four-pole diode-ladder VCF using transistors as diodes, with extra resonance artifacts revealed by Tim Stinchcombe on his excellent website. Tim Stinchcombe - TB-303 Diode Ladder Filter model
| | | | Tim Stinchcombe - TB-303 Diode Ladder Filter model
|
|
|
Meanwhile, if you want to go deeper with regards to 4-pole filter topologies (and lowpass/highpass configurations) it is worth checking out a paper published in 1985 - http://electronotes.netfirms.com/EN85VCF.PDF The easiest way to think about it, from this paper, is that you think about each stage as an inversion, and the input itself is one of the stages, so for a 4-pole filter there are 4+1 inversion stages. But in the digital world I guess you'll have to test input and output at a relatively low frequency to the cutoff to determine inversion principles for the enhancement of resonance.
I hope this helps. It gave me a break from mixing! Ed _-_-_-_-_-_-_-^-_-_-_-_-_-_-_ For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston <williamahuston@gmail.com> wrote:
What's the best or "correct" way to add resonance to a [vcf~]?
Should the feedback be delayed?
Should the feedback be inverted?
Should the feedback be from the outlet I'm using?
Or should the feedback always come from the BP or HiPass side?
Thanks!BH
-- William Huston: WilliamAHuston@gmail.com Binghamton NY
Public Service Mapping / Videography / Research Blog -- Facebook -- Twitter -- Youtube Document collections: VirtualPipelines -- BHDCSDimockArchive Please support my work: TinyURL.com/DonateToBillHuston
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list
Ach! NO! inversion does not happen at the input! I guess you can look at the topologies and discover for yourself.
I'm having a bad week. x Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 14:33:13 GMT+1, Ed Kelly <morph_2016@yahoo.co.uk> wrote:
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics... If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (http://www.birthofasynth.com/Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf) you will see that the signal path from input to output goes through 5 inversion stages before being fed back into the input to generate resonance. Therefore it is inverted.
Since most (resonant) filters consist of an even number of stages (and therefore an even number of poles and/or zeroes) you should probably invert the feedback. With an odd number you should probably not invert feedback. My guess is that vcf~ implements an even-number (probably 4-pole) resonant filter, a la Moog. You can also try mvcf~ from my library (ekext - http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about.
This might seem counter-intuitive, but the image below shows how this works with regards to vcf~ - the output of vcf~ is NOT inverted, whereas the output of an analog VCF should be.
Odd-number staged filters are very rare in the analog world, and most (i.e. 18dB per octave) were created to implement the (mythical 3-pole topology) filter of the Roland TB303. However, according to the schematics of the TB303 it is a four-pole diode-ladder VCF using transistors as diodes, with extra resonance artifacts revealed by Tim Stinchcombe on his excellent website. Tim Stinchcombe - TB-303 Diode Ladder Filter model
| | | | Tim Stinchcombe - TB-303 Diode Ladder Filter model
|
|
|
Meanwhile, if you want to go deeper with regards to 4-pole filter topologies (and lowpass/highpass configurations) it is worth checking out a paper published in 1985 - http://electronotes.netfirms.com/EN85VCF.PDF The easiest way to think about it, from this paper, is that you think about each stage as an inversion, and the input itself is one of the stages, so for a 4-pole filter there are 4+1 inversion stages. But in the digital world I guess you'll have to test input and output at a relatively low frequency to the cutoff to determine inversion principles for the enhancement of resonance.
I hope this helps. It gave me a break from mixing! Ed _-_-_-_-_-_-_-^-_-_-_-_-_-_-_ For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston <williamahuston@gmail.com> wrote:
What's the best or "correct" way to add resonance to a [vcf~]?
Should the feedback be delayed?
Should the feedback be inverted?
Should the feedback be from the outlet I'm using?
Or should the feedback always come from the BP or HiPass side?
Thanks!BH
-- William Huston: WilliamAHuston@gmail.com Binghamton NY
Public Service Mapping / Videography / Research Blog -- Facebook -- Twitter -- Youtube Document collections: VirtualPipelines -- BHDCSDimockArchive Please support my work: TinyURL.com/DonateToBillHuston
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/listinfo/pd-list
The 4-pole model in the ENS-85 paper does not have inversion at the input, but the Thomas Henry 2-pole design does. So I guess the 4-pole is more similar to vcf~
go figure. Signing off Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 14:40:20 GMT+1, Ed Kelly via Pd-list <pd-list@lists.iem.at> wrote:
Ach! NO! inversion does not happen at the input! I guess you can look at the topologies and discover for yourself.
I'm having a bad week. x Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 14:33:13 GMT+1, Ed Kelly <morph_2016@yahoo.co.uk> wrote:
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics... If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (http://www.birthofasynth.com/Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf) you will see that the signal path from input to output goes through 5 inversion stages before being fed back into the input to generate resonance. Therefore it is inverted.
Since most (resonant) filters consist of an even number of stages (and therefore an even number of poles and/or zeroes) you should probably invert the feedback. With an odd number you should probably not invert feedback. My guess is that vcf~ implements an even-number (probably 4-pole) resonant filter, a la Moog. You can also try mvcf~ from my library (ekext - http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about.
This might seem counter-intuitive, but the image below shows how this works with regards to vcf~ - the output of vcf~ is NOT inverted, whereas the output of an analog VCF should be.
Odd-number staged filters are very rare in the analog world, and most (i.e. 18dB per octave) were created to implement the (mythical 3-pole topology) filter of the Roland TB303. However, according to the schematics of the TB303 it is a four-pole diode-ladder VCF using transistors as diodes, with extra resonance artifacts revealed by Tim Stinchcombe on his excellent website. Tim Stinchcombe - TB-303 Diode Ladder Filter model
| | | | Tim Stinchcombe - TB-303 Diode Ladder Filter model
|
|
|
Meanwhile, if you want to go deeper with regards to 4-pole filter topologies (and lowpass/highpass configurations) it is worth checking out a paper published in 1985 - http://electronotes.netfirms.com/EN85VCF.PDF The easiest way to think about it, from this paper, is that you think about each stage as an inversion, and the input itself is one of the stages, so for a 4-pole filter there are 4+1 inversion stages. But in the digital world I guess you'll have to test input and output at a relatively low frequency to the cutoff to determine inversion principles for the enhancement of resonance.
I hope this helps. It gave me a break from mixing! Ed _-_-_-_-_-_-_-^-_-_-_-_-_-_-_ For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston <williamahuston@gmail.com> wrote:
What's the best or "correct" way to add resonance to a [vcf~]?
Should the feedback be delayed?
Should the feedback be inverted?
Should the feedback be from the outlet I'm using?
Or should the feedback always come from the BP or HiPass side?
Thanks!BH
-- William Huston: WilliamAHuston@gmail.com Binghamton NY
Public Service Mapping / Videography / Research Blog -- Facebook -- Twitter -- Youtube Document collections: VirtualPipelines -- BHDCSDimockArchive Please support my work: TinyURL.com/DonateToBillHuston
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
Well, regardless of the correct number of inversions, some informative and well linked posts there - cheers for that Ed :)
On 24 April 2018 at 20:44, Ed Kelly via Pd-list pd-list@lists.iem.at wrote:
The 4-pole model in the ENS-85 paper does not have inversion at the input, but the Thomas Henry 2-pole design does. So I guess the 4-pole is more similar to vcf~
go figure. Signing off Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For *Lone Shark *releases, *Pure Data *software and published *Research*, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 14:40:20 GMT+1, Ed Kelly via Pd-list < pd-list@lists.iem.at> wrote:
Ach! NO! inversion does not happen at the input! I guess you can look at the topologies and discover for yourself.
I'm having a bad week. x Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For *Lone Shark *releases, *Pure Data *software and published *Research*, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 14:33:13 GMT+1, Ed Kelly < morph_2016@yahoo.co.uk> wrote:
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics...
If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (http://www.birthofasynth.com/ Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf) you will see that the signal path from input to output goes through 5 inversion stages before being fed back into the input to generate resonance. Therefore it is inverted.
Since most (resonant) filters consist of an even number of stages (and therefore an even number of poles and/or zeroes) you should probably invert the feedback. With an odd number you should probably not invert feedback. My guess is that vcf~ implements an even-number (probably 4-pole) resonant filter, a la Moog. You can also try mvcf~ from my library (ekext - http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about.
This might seem counter-intuitive, but the image below shows how this works with regards to vcf~ - the output of vcf~ is NOT inverted, whereas the output of an analog VCF should be.
Odd-number staged filters are very rare in the analog world, and most (i.e. 18dB per octave) were created to implement the (mythical 3-pole topology) filter of the Roland TB303. However, according to the schematics of the TB303 it is a four-pole diode-ladder VCF using transistors as diodes, with extra resonance artifacts revealed by Tim Stinchcombe on his excellent website. Tim Stinchcombe - TB-303 Diode Ladder Filter model http://www.timstinchcombe.co.uk/index.php?pge=diode2
Tim Stinchcombe - TB-303 Diode Ladder Filter model
http://www.timstinchcombe.co.uk/index.php?pge=diode2
Meanwhile, if you want to go deeper with regards to 4-pole filter topologies (and lowpass/highpass configurations) it is worth checking out a paper published in 1985 - http://electronotes.netfirms.com/EN85VCF.PDF
The easiest way to think about it, from this paper, is that you think about each stage as an inversion, and the input itself is one of the stages, so for a 4-pole filter there are 4+1 inversion stages. But in the digital world I guess you'll have to test input and output at a relatively low frequency to the cutoff to determine inversion principles for the enhancement of resonance.
I hope this helps. It gave me a break from mixing! Ed _-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For *Lone Shark *releases, *Pure Data *software and published *Research*, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston < williamahuston@gmail.com> wrote:
What's the best or "correct" way to add resonance to a [vcf~]?
- Should the feedback be delayed?
- Should the feedback be inverted?
- Should the feedback be from the outlet I'm using?
- Or should the feedback always come from the BP or HiPass side?
Thanks! BH
-- William Huston: WilliamAHuston@gmail.com Binghamton NY
*Public Service Mapping / Videography / Research* Blog http://WilliamAHuston.blogspot.com -- Facebook http://facebook.com/billhuston -- Twitter http://twitter.com/WilliamAHuston-- Youtube https://www.youtube.com/channel/UCGijK1amWOLglT3YeTyEBNQ?sub_congfirmation=1 Document collections: VirtualPipelines http://TinyURL.com/VirtualPipelines -- BHDCSDimockArchive http://bit.ly/BHDCSDimockArchive Please support my work: TinyURL.com/DonateToBillHuston
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
Yes, thanks for the detailed response, Ed!
I was hoping for some guidance for a bolt-on method for adding resonance to vcf~, but maybe it's not so easy? or the wrong approach?
My error was thinking resonance was implemented with feedback.
From this video, it looks like resonance is caused by a bump in the filter
shape at the cutoff frequency: https://youtu.be/XA_WnyA7D6k
This looks like a shape that naturally occurs in analogue circuits.
Someone in the FB group suggested [svf~] from Cyclone. It's really great, as it gives you HiP, LoP, BP, and Band Reject(!!).
I would be in Filter Heaven if that had adjustable Q...
PS: Can someone remind me of the filters where you can set parameters like cutoff freq at *audio rate*?
Thanks! BH
On Wed, Apr 25, 2018, 11:09 AM Julian Brooks jbeezez@gmail.com wrote:
Well, regardless of the correct number of inversions, some informative and well linked posts there - cheers for that Ed :)
On 24 April 2018 at 20:44, Ed Kelly via Pd-list pd-list@lists.iem.at wrote:
The 4-pole model in the ENS-85 paper does not have inversion at the input, but the Thomas Henry 2-pole design does. So I guess the 4-pole is more similar to vcf~
go figure. Signing off Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For *Lone Shark *releases, *Pure Data *software and published *Research*, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 14:40:20 GMT+1, Ed Kelly via Pd-list < pd-list@lists.iem.at> wrote:
Ach! NO! inversion does not happen at the input! I guess you can look at the topologies and discover for yourself.
I'm having a bad week. x Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For *Lone Shark *releases, *Pure Data *software and published *Research*, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 14:33:13 GMT+1, Ed Kelly < morph_2016@yahoo.co.uk> wrote:
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics...
If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (http://www.birthofasynth.com/ Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf) you will see that the signal path from input to output goes through 5 inversion stages before being fed back into the input to generate resonance. Therefore it is inverted.
Since most (resonant) filters consist of an even number of stages (and therefore an even number of poles and/or zeroes) you should probably invert the feedback. With an odd number you should probably not invert feedback. My guess is that vcf~ implements an even-number (probably 4-pole) resonant filter, a la Moog. You can also try mvcf~ from my library (ekext - http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about.
This might seem counter-intuitive, but the image below shows how this works with regards to vcf~ - the output of vcf~ is NOT inverted, whereas the output of an analog VCF should be.
Odd-number staged filters are very rare in the analog world, and most (i.e. 18dB per octave) were created to implement the (mythical 3-pole topology) filter of the Roland TB303. However, according to the schematics of the TB303 it is a four-pole diode-ladder VCF using transistors as diodes, with extra resonance artifacts revealed by Tim Stinchcombe on his excellent website. Tim Stinchcombe - TB-303 Diode Ladder Filter model http://www.timstinchcombe.co.uk/index.php?pge=diode2
Tim Stinchcombe - TB-303 Diode Ladder Filter model
http://www.timstinchcombe.co.uk/index.php?pge=diode2
Meanwhile, if you want to go deeper with regards to 4-pole filter topologies (and lowpass/highpass configurations) it is worth checking out a paper published in 1985 - http://electronotes.netfirms.com/EN85VCF.PDF
The easiest way to think about it, from this paper, is that you think about each stage as an inversion, and the input itself is one of the stages, so for a 4-pole filter there are 4+1 inversion stages. But in the digital world I guess you'll have to test input and output at a relatively low frequency to the cutoff to determine inversion principles for the enhancement of resonance.
I hope this helps. It gave me a break from mixing! Ed _-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For *Lone Shark *releases, *Pure Data *software and published *Research*, go to http://sharktracks.co.uk
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston < williamahuston@gmail.com> wrote:
What's the best or "correct" way to add resonance to a [vcf~]?
- Should the feedback be delayed?
- Should the feedback be inverted?
- Should the feedback be from the outlet I'm using?
- Or should the feedback always come from the BP or HiPass side?
Thanks! BH
-- William Huston: WilliamAHuston@gmail.com Binghamton NY
*Public Service Mapping / Videography / Research* Blog http://WilliamAHuston.blogspot.com -- Facebook http://facebook.com/billhuston -- Twitter http://twitter.com/WilliamAHuston-- Youtube https://www.youtube.com/channel/UCGijK1amWOLglT3YeTyEBNQ?sub_congfirmation=1 Document collections: VirtualPipelines http://TinyURL.com/VirtualPipelines -- BHDCSDimockArchive http://bit.ly/BHDCSDimockArchive Please support my work: TinyURL.com/DonateToBillHuston
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/li stinfo/pd-list _______________________________________________ Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/li stinfo/pd-list
Pd-list@lists.iem.at mailing list UNSUBSCRIBE and account-management -> https://lists.puredata.info/li stinfo/pd-list
Hi William,
both [vcf~] and [svf~] let you set the cutoff frequency at audio rate and both have adjustable Q... what are you missing exactly?
the vcf_* filters in iemlib are all suited for audio rate modulations.
for moog style lowpass filters have a look at [bob~] and [ggee/moog~].
Christof
Gesendet: Mittwoch, 25. April 2018 um 18:46 Uhr Von: "William Huston" williamahuston@gmail.com An: "Julian Brooks" jbeezez@gmail.com Cc: "pd-list@lists.iem.at" pd-list@lists.iem.at Betreff: Re: [PD] [vcf~] with resonance?
Yes, thanks for the detailed response, Ed! I was hoping for some guidance for a bolt-on method for adding resonance to vcf~, but maybe it's not so easy? or the wrong approach? My error was thinking resonance was implemented with feedback.
From this video, it looks like resonance is caused by a bump in the filter shape at the cutoff frequency:
https://youtu.be/XA_WnyA7D6k This looks like a shape that naturally occurs in analogue circuits. Someone in the FB group suggested [svf~] from Cyclone. It's really great, as it gives you HiP, LoP, BP, and Band Reject(!!). I would be in Filter Heaven if that had adjustable Q... PS: Can someone remind me of the filters where you can set parameters like cutoff freq at *audio rate*? Thanks! BH
On Wed, Apr 25, 2018, 11:09 AM Julian Brooks <jbeezez@gmail.com[mailto:jbeezez@gmail.com]> wrote: Well, regardless of the correct number of inversions, some informative and well linked posts there - cheers for that Ed :) On 24 April 2018 at 20:44, Ed Kelly via Pd-list <pd-list@lists.iem.at[mailto:pd-list@lists.iem.at]> wrote:
The 4-pole model in the ENS-85 paper does not have inversion at the input, but the Thomas Henry 2-pole design does. So I guess the 4-pole is more similar to vcf~ go figure. Signing off Ed _-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk%5Bhttp://sharktracks.co.uk]
On Tuesday, 24 April 2018, 14:40:20 GMT+1, Ed Kelly via Pd-list <pd-list@lists.iem.at[mailto:pd-list@lists.iem.at]> wrote:
Ach! NO! inversion does not happen at the input! I guess you can look at the topologies and discover for yourself. I'm having a bad week. x Ed _-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk%5Bhttp://sharktracks.co.uk]
On Tuesday, 24 April 2018, 14:33:13 GMT+1, Ed Kelly <morph_2016@yahoo.co.uk[mailto:morph_2016@yahoo.co.uk]> wrote:
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics... If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (http://www.birthofasynth.com/Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf%5Bhttp://...]) you will see that the signal path from input to output goes through 5 inversion stages before being fed back into the input to generate resonance. Therefore it is inverted.
Since most (resonant) filters consist of an even number of stages (and therefore an even number of poles and/or zeroes) you should probably invert the feedback. With an odd number you should probably not invert feedback. My guess is that vcf~ implements an even-number (probably 4-pole) resonant filter, a la Moog. You can also try mvcf~ from my library (ekext - http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz%5Bhttp://sharktracks.co...]) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about. This might seem counter-intuitive, but the image below shows how this works with regards to vcf~ - the output of vcf~ is NOT inverted, whereas the output of an analog VCF should be. Odd-number staged filters are very rare in the analog world, and most (i.e. 18dB per octave) were created to implement the (mythical 3-pole topology) filter of the Roland TB303. However, according to the schematics of the TB303 it is a four-pole diode-ladder VCF using transistors as diodes, with extra resonance artifacts revealed by Tim Stinchcombe on his excellent website. Tim Stinchcombe - TB-303 Diode Ladder Filter model[http://www.timstinchcombe.co.uk/index.php?pge=diode2]
Tim Stinchcombe - TB-303 Diode Ladder Filter model[http://www.timstinchcombe.co.uk/index.php?pge=diode2]
Meanwhile, if you want to go deeper with regards to 4-pole filter topologies (and lowpass/highpass configurations) it is worth checking out a paper published in 1985 - http://electronotes.netfirms.com/EN85VCF.PDF%5Bhttp://electronotes.netfirms....]
The easiest way to think about it, from this paper, is that you think about each stage as an inversion, and the input itself is one of the stages, so for a 4-pole filter there are 4+1 inversion stages. But in the digital world I guess you'll have to test input and output at a relatively low frequency to the cutoff to determine inversion principles for the enhancement of resonance. I hope this helps. It gave me a break from mixing! Ed_-_-_-_-_-_-_-^-_-_-_-_-_-_-_ For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk%5Bhttp://sharktracks.co.uk]
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston <williamahuston@gmail.com[mailto:williamahuston@gmail.com]> wrote:
What's the best or "correct" way to add resonance to a [vcf~]? Should the feedback be delayed?Should the feedback be inverted?Should the feedback be from the outlet I'm using? Or should the feedback always come from the BP or HiPass side?
Thanks! BH
-- William Huston: WilliamAHuston@gmail.com[mailto:WilliamAHuston@gmail.com] Binghamton NY
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Thanks Christof.
The help file for [svf~] shows a control-rate number box feeding the cutoff. But I tested with [sig~] and it works. Thanks.
However I see no mention in the help of [scf~] for how to set Q. Cutoff and Resonance only.
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On Wed, Apr 25, 2018 at 1:38 PM, Christof Ressi christof.ressi@gmx.at wrote:
Hi William,
both [vcf~] and [svf~] let you set the cutoff frequency at audio rate and both have adjustable Q... what are you missing exactly?
the vcf_* filters in iemlib are all suited for audio rate modulations.
for moog style lowpass filters have a look at [bob~] and [ggee/moog~].
Christof
Gesendet: Mittwoch, 25. April 2018 um 18:46 Uhr Von: "William Huston" williamahuston@gmail.com An: "Julian Brooks" jbeezez@gmail.com Cc: "pd-list@lists.iem.at" pd-list@lists.iem.at Betreff: Re: [PD] [vcf~] with resonance?
Yes, thanks for the detailed response, Ed!
I was hoping for some guidance for a bolt-on method for adding resonance to vcf~, but maybe it's not so easy? or the wrong approach?
My error was thinking resonance was implemented with feedback.
From this video, it looks like resonance is caused by a bump in the filter shape at the cutoff frequency:
This looks like a shape that naturally occurs in analogue circuits. Someone in the FB group suggested [svf~] from Cyclone. It's really great, as it gives you HiP, LoP, BP, and Band Reject(!!).
I would be in Filter Heaven if that had adjustable Q...
PS: Can someone remind me of the filters where you can set parameters like cutoff freq at *audio rate*?
Thanks! BH
On Wed, Apr 25, 2018, 11:09 AM Julian Brooks <jbeezez@gmail.com[mailto: jbeezez@gmail.com]> wrote: Well, regardless of the correct number of inversions, some informative and well linked posts there - cheers for that Ed :)
On 24 April 2018 at 20:44, Ed Kelly via Pd-list <pd-list@lists.iem.at [mailto:pd-list@lists.iem.at]> wrote:
The 4-pole model in the ENS-85 paper does not have inversion at the input, but the Thomas Henry 2-pole design does. So I guess the 4-pole is more similar to vcf~
go figure. Signing off Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk%5Bhttp://sharktracks.co.uk]
On Tuesday, 24 April 2018, 14:40:20 GMT+1, Ed Kelly via Pd-list < pd-list@lists.iem.at[mailto:pd-list@lists.iem.at]> wrote:
Ach! NO! inversion does not happen at the input! I guess you can look at the topologies and discover for yourself.
I'm having a bad week. x Ed
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_
For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk%5Bhttp://sharktracks.co.uk]
On Tuesday, 24 April 2018, 14:33:13 GMT+1, Ed Kelly < morph_2016@yahoo.co.uk[mailto:morph_2016@yahoo.co.uk]> wrote:
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics...
If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (http://www.birthofasynth.com/ Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf[http://www.birthofasynth.com/Thomas_ Henry/pdf/VCF-1/Sheet_0002.pdf]) you will see that the signal path from input to output goes through 5 inversion stages before being fed back into the input to generate resonance. Therefore it is inverted.
Since most (resonant) filters consist of an even number of stages (and therefore an even number of poles and/or zeroes) you should probably invert the feedback. With an odd number you should probably not invert feedback. My guess is that vcf~ implements an even-number (probably 4-pole) resonant filter, a la Moog. You can also try mvcf~ from my library (ekext - http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz%5B http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz]) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about. This might seem counter-intuitive, but the image below shows how this works with regards to vcf~ - the output of vcf~ is NOT inverted, whereas the output of an analog VCF should be. Odd-number staged filters are very rare in the analog world, and most (i.e. 18dB per octave) were created to implement the (mythical 3-pole topology) filter of the Roland TB303. However, according to the schematics of the TB303 it is a four-pole diode-ladder VCF using transistors as diodes, with extra resonance artifacts revealed by Tim Stinchcombe on his excellent website. Tim Stinchcombe - TB-303 Diode Ladder Filter model[ http://www.timstinchcombe.co.uk/index.php?pge=diode2]
Tim Stinchcombe - TB-303 Diode Ladder Filter model[http://www. timstinchcombe.co.uk/index.php?pge=diode2]
Meanwhile, if you want to go deeper with regards to 4-pole filter topologies (and lowpass/highpass configurations) it is worth checking out a paper published in 1985 - http://electronotes.netfirms. com/EN85VCF.PDF[http://electronotes.netfirms.com/EN85VCF.PDF]
The easiest way to think about it, from this paper, is that you think about each stage as an inversion, and the input itself is one of the stages, so for a 4-pole filter there are 4+1 inversion stages. But in the digital world I guess you'll have to test input and output at a relatively low frequency to the cutoff to determine inversion principles for the enhancement of resonance.
I hope this helps. It gave me a break from mixing! Ed_-_-_-_-_-_-_-^-_-_-_-_-_-_-_ For Lone Shark releases, Pure Data software and published Research, go to http://sharktracks.co.uk%5Bhttp://sharktracks.co.uk]
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston < williamahuston@gmail.com[mailto:williamahuston@gmail.com]> wrote:
What's the best or "correct" way to add resonance to a [vcf~]? Should the feedback be delayed?Should the feedback be inverted?Should the feedback be from the outlet I'm using? Or should the feedback always come from the BP or HiPass side?
Thanks! BH
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2018-04-25 15:03 GMT-03:00 William Huston williamahuston@gmail.com:
Thanks Christof.
The help file for [svf~] shows a control-rate number box feeding the cutoff. But I tested with [sig~] and it works. Thanks.
the documentation (at least the current one) specifies all kinds of data each inlets receives, and it says it takes floats/signals in every inlet.
However I see no mention in the help of [scf~] for how to set Q.
the documentation (again, the current one) for cyclone/svf~ tells you the Q/resonance is set via the 3rd inlet
Q refers to the bandwidth of a resonant filter, but is ultimate effect t depends on what kind of filter we're talking about. In some filters, adjusting the bandwidth also boost the resonant frequency. This is not the case of vcf~, which acts more like a constant gain bandpass filter. It's more common in electronic music to have a lowpass resonant filter, though, like the bob~ object, which emulates a moog filter.
So if you wanna make [vcf~] to have a higher boost in the resonant frequency, just add some gain to it...
The [svf~] object has such kind of lowpass resonant filters. Cyclone also has other filters, [lores~] is also a lowpass resonant filter, but it frequency response varies with frequency (which I think is bad). Now, [reson~] is a bandpass filter where you can adjust the bandwidth and overall gain. A new couple of objects in cyclone are [filtercoeff~] and [biquad~], which allow you to have a more proper lowpass resonant filter, controlled via signals.
I actually think the [filtercoeff~] + [biquad~] design is terrible. It'd be much simpler just to have ready made filters. So I made them in mey new library, for instance: [else/lowpass~].
cheers
On Wed, Apr 25, 2018 at 12:46 PM, William Huston williamahuston@gmail.com wrote:
Yes, thanks for the detailed response, Ed!
I was hoping for some guidance for a bolt-on method for adding resonance to vcf~, but maybe it's not so easy? or the wrong approach?
My error was thinking resonance was implemented with feedback.
I don't think you were wrong.
From this video, it looks like resonance is caused by a bump in the filter shape at the cutoff frequency: https://youtu.be/XA_WnyA7D6k
The bump in the filter response is a manifestation of resonance caused by
feedback (the electronotes paper explains it as moving the poles toward the imaginary axis as feedback increases).
An analog-synth-like filter can be made with 4 [lop~]s in series with a [send~] at the output and a [receive~] | [*~ -0.9] <-change this number to set resonance (between 0 and -1) | [clip~ -1 1] <- stops it from blowing up, but gives distortion with too much feedback | on the input. The main problem is that the resonance value changes with filter cutoff frequency. Also Pd's number boxes don't have fine enough resolution; I use negative values from 0-20000 then divide by 10000 to get better control.
Martin
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Christof Ressi -
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William Huston