<div dir="ltr"><div><div><div><div>Thanks Christof.<br><br></div>The help file for [svf~] shows a control-rate number box feeding the cutoff.<br></div>But I tested with [sig~] and it works. Thanks.<br><br></div>However I see no mention in the help of [scf~] for how to set Q. <br></div>Cutoff and Resonance only. <br></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div>--<br>William Huston: <a href="mailto:WilliamAHuston@gmail.com" target="_blank">WilliamAHuston@gmail.com</a><br>Binghamton NY<br><div style="text-align:center"><div style="text-align:center"><span></span><br><span><b>Public Service Mapping / Videography / Research</b></span><br><span></span><a href="http://WilliamAHuston.blogspot.com" target="_blank">Blog</a> -- <a href="http://facebook.com/billhuston" target="_blank">Facebook</a> -- <a href="http://twitter.com/WilliamAHuston" target="_blank">Twitter </a><span><span><span>-- <a href="https://www.youtube.com/channel/UCGijK1amWOLglT3YeTyEBNQ?sub_congfirmation=1" target="_blank">Youtube</a></span></span></span><br><span><span><span></span></span></span>Document collections: <a href="http://TinyURL.com/VirtualPipelines" target="_blank">VirtualPipelines</a> -- <a href="http://bit.ly/BHDCSDimockArchive" target="_blank">BHDCSDimockArchive</a><br><span><span>Please support my work: <a href="http://TinyURL.com/DonateToBillHuston" target="_blank">TinyURL.com/DonateToBillHuston</a></span></span><br></div><span><span></span></span></div><span><br></span></div><div><br></div></div></div></div></div></div>
<br><div class="gmail_quote">On Wed, Apr 25, 2018 at 1:38 PM, Christof Ressi <span dir="ltr"><<a href="mailto:christof.ressi@gmx.at" target="_blank">christof.ressi@gmx.at</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi William,<br>
<br>
both [vcf~] and [svf~] let you set the cutoff frequency at audio rate and both have adjustable Q... what are you missing exactly? <br>
<br>
the vcf_* filters in iemlib are all suited for audio rate modulations.<br>
<br>
for moog style lowpass filters have a look at [bob~] and [ggee/moog~]. <br>
<br>
Christof<br>
<br>
<br>
<br>
Gesendet: Mittwoch, 25. April 2018 um 18:46 Uhr<br>
Von: "William Huston" <<a href="mailto:williamahuston@gmail.com">williamahuston@gmail.com</a>><br>
An: "Julian Brooks" <<a href="mailto:jbeezez@gmail.com">jbeezez@gmail.com</a>><br>
Cc: "<a href="mailto:pd-list@lists.iem.at">pd-list@lists.iem.at</a>" <<a href="mailto:pd-list@lists.iem.at">pd-list@lists.iem.at</a>><br>
Betreff: Re: [PD] [vcf~] with resonance?<br>
<span class=""><br>
Yes, thanks for the detailed response, Ed!<br>
<br>
I was hoping for some guidance for a bolt-on method for adding resonance to vcf~,<br>
but maybe it's not so easy? or the wrong approach?<br>
<br>
My error was thinking resonance was implemented with feedback.<br>
<br>
>From this video, it looks like resonance is caused by a bump in the filter shape at the cutoff frequency:<br>
<br>
<a href="https://youtu.be/XA_WnyA7D6k" rel="noreferrer" target="_blank">https://youtu.be/XA_WnyA7D6k</a><br>
<br>
This looks like a shape that naturally occurs in analogue circuits. <br>
Someone in the FB group suggested [svf~] from Cyclone.<br>
It's really great, as it gives you HiP, LoP, BP, and Band Reject(!!).<br>
<br>
I would be in Filter Heaven if that had adjustable Q...<br>
<br>
PS: Can someone remind me of the filters where you can set parameters like cutoff freq at *audio rate*?<br>
<br>
Thanks!<br>
BH<br>
<br>
<br>
<br>
<br>
</span><span class="">On Wed, Apr 25, 2018, 11:09 AM Julian Brooks <<a href="mailto:jbeezez@gmail.com">jbeezez@gmail.com</a>[mailto:<a href="mailto:jbeezez@gmail.com">jbee<wbr>zez@gmail.com</a>]> wrote:<br>
Well, regardless of the correct number of inversions, some informative and well linked posts there - cheers for that Ed :)<br>
<br>
</span><span class="">On 24 April 2018 at 20:44, Ed Kelly via Pd-list <<a href="mailto:pd-list@lists.iem.at">pd-list@lists.iem.at</a>[mailto:<a href="mailto:pd-list@lists.iem.at">p<wbr>d-list@lists.iem.at</a>]> wrote:<br>
<br>
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~<br>
<br>
go figure.<br>
Signing off<br>
Ed<br>
<br>
<br>
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_<br>
<br>
</span>For Lone Shark releases, Pure Data software and published Research, go to <a href="http://sharktracks.co.uk" rel="noreferrer" target="_blank">http://sharktracks.co.uk</a>[<a href="http://sharktracks.co.uk" rel="noreferrer" target="_blank">http:<wbr>//sharktracks.co.uk</a>] <br>
<span class=""><br>
<br>
<br>
<br>
On Tuesday, 24 April 2018, 14:40:20 GMT+1, Ed Kelly via Pd-list <<a href="mailto:pd-list@lists.iem.at">pd-list@lists.iem.at</a>[mailto:<a href="mailto:pd-list@lists.iem.at">p<wbr>d-list@lists.iem.at</a>]> wrote:<br>
<br>
<br>
<br>
Ach! NO! inversion does not happen at the input!<br>
I guess you can look at the topologies and discover for yourself.<br>
<br>
I'm having a bad week.<br>
x<br>
Ed<br>
<br>
<br>
_-_-_-_-_-_-_-^-_-_-_-_-_-_-_<br>
<br>
</span>For Lone Shark releases, Pure Data software and published Research, go to <a href="http://sharktracks.co.uk" rel="noreferrer" target="_blank">http://sharktracks.co.uk</a>[<a href="http://sharktracks.co.uk" rel="noreferrer" target="_blank">http:<wbr>//sharktracks.co.uk</a>] <br>
<span class=""> <br>
<br>
<br>
On Tuesday, 24 April 2018, 14:33:13 GMT+1, Ed Kelly <<a href="mailto:morph_2016@yahoo.co.uk">morph_2016@yahoo.co.uk</a>[<wbr>mailto:<a href="mailto:morph_2016@yahoo.co.uk">morph_2016@yahoo.co.uk</a>]<wbr>> wrote:<br>
<br>
<br>
<br>
Correct me if I'm wrong (and I'm sure someone will) but going back to analog electronics...<br>
<br>
</span>If you examine the topology of a standard analog filter design, such as the Thomas Henry VCF1 (<a href="http://www.birthofasynth.com/Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf[http://www.birthofasynth.com/Thomas_Henry/pdf/VCF-1/Sheet_0002.pdf]" rel="noreferrer" target="_blank">http://www.birthofasynth.com/<wbr>Thomas_Henry/pdf/VCF-1/Sheet_<wbr>0002.pdf[http://www.<wbr>birthofasynth.com/Thomas_<wbr>Henry/pdf/VCF-1/Sheet_0002.<wbr>pdf]</a>) 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.<br>
<br>
<br>
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 - <a href="http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz[http://sharktracks.co.uk/puredata/ekext-0.1.8.tar.gz]" rel="noreferrer" target="_blank">http://sharktracks.co.uk/<wbr>puredata/ekext-0.1.8.tar.gz[<wbr>http://sharktracks.co.uk/<wbr>puredata/ekext-0.1.8.tar.gz]</a>) which is another attempt at emulating this topology, or there are lots of others I'm sure you know about.<br>
<span class="">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.<br>
</span>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[<a href="http://www.timstinchcombe.co.uk/index.php?pge=diode2" rel="noreferrer" target="_blank">http://www.<wbr>timstinchcombe.co.uk/index.<wbr>php?pge=diode2</a>]<br>
<br>
<br>
<br>
Tim Stinchcombe - TB-303 Diode Ladder Filter model[<a href="http://www.timstinchcombe.co.uk/index.php?pge=diode2" rel="noreferrer" target="_blank">http://www.<wbr>timstinchcombe.co.uk/index.<wbr>php?pge=diode2</a>]<br>
<br>
<br>
<br>
<br>
<br>
<br>
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 - <a href="http://electronotes.netfirms.com/EN85VCF.PDF[http://electronotes.netfirms.com/EN85VCF.PDF]" rel="noreferrer" target="_blank">http://electronotes.netfirms.<wbr>com/EN85VCF.PDF[http://<wbr>electronotes.netfirms.com/<wbr>EN85VCF.PDF]</a><br>
<span class=""><br>
<br>
<br>
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.<br>
<br>
I hope this helps. It gave me a break from mixing!<br>
Ed_-_-_-_-_-_-_-^-_-_-_-_-_-_-<wbr>_<br>
</span>For Lone Shark releases, Pure Data software and published Research, go to <a href="http://sharktracks.co.uk" rel="noreferrer" target="_blank">http://sharktracks.co.uk</a>[<a href="http://sharktracks.co.uk" rel="noreferrer" target="_blank">http:<wbr>//sharktracks.co.uk</a>] <br>
<span class=""> <br>
<br>
<br>
On Tuesday, 24 April 2018, 06:44:19 GMT+1, William Huston <<a href="mailto:williamahuston@gmail.com">williamahuston@gmail.com</a>[<wbr>mailto:<a href="mailto:williamahuston@gmail.com">williamahuston@gmail.<wbr>com</a>]> wrote:<br>
<br>
<br>
<br>
What's the best or "correct" way to add resonance to a [vcf~]?<br>
</span>Should the feedback be delayed?Should the feedback be inverted?Should the feedback be from the outlet I'm using?<br>
<span class="">Or should the feedback always come from the BP or HiPass side?<br>
<br>
Thanks!<br>
BH<br>
<br>
<br>
--<br>
</span>William Huston: <a href="mailto:WilliamAHuston@gmail.com">WilliamAHuston@gmail.com</a>[<wbr>mailto:<a href="mailto:WilliamAHuston@gmail.com">WilliamAHuston@gmail.<wbr>com</a>]<br>
<span class="">Binghamton NY<br>
<br>
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</blockquote></div><br></div>