[Csnd] Butterworth filters and signal splitting

[Csnd] Butterworth filters and signal splitting

Date	2024-12-14 00:25
From	"Jeanette C."
Subject	[Csnd] Butterworth filters and signal splitting
	Hey hey, I am just experimenting with multiband stuff. I try to split a signal into three or four bands. The lowest band uses a lowpass filter and the highest a ighpass filter. In between there should be one or two bandpass filters. I have started work with Butterworth filters. I try to filter the signal so, that the outputs of the filters, taken together, (nearly) reconstruct the original signal. I am not set on the Butterworth filters and the crossing points in the setup below, can be purely nominal. They don't actually have to represent a frequency of one of the filters, if it makes all the calculations easier. So, I have some issues with half-power points. Here's my current setup, with a few hardcoded values. iCross1 init 200 ; nominal lowpass frequency iCross2 init 800 ; nominal highpass frequency iCentre init (iCross1 + iCross2) / 2 ; the mid-point between the two iBandwidth init (iCross2 - iCross1) * 2 ; The bandwidth The output sounds not too bad. But there are issues. A bandwidth of 1200 with a centre of 500 would result in a negative frequency for the lower "edge" of teh bandpass filter. I was working from the following, possibly wrong or misunderstood, example: a second-order Butterworth Bandpass filter centred at 400Hz with a bandwidth of 400 has the half-power points at 300Hz and 500Hz. So I'd assume that it would have the half-power points at 200Hz and 600Hz with a bandwidth of 800. Can anyone suggest a better approach or point out my wooly thinking, please? Best wishes, Jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c There's no time to loose And next week, You might not see me here <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here

Date	2024-12-14 12:42
From	Oeyvind Brandtsegg
Subject	Re: [Csnd] Butterworth filters and signal splitting
	Hi Jeanette, It looks like your estimation of crossover frequencies are off (or at least different than what I think). You write "a second-order Butterworth Bandpass filter centred at 400Hz with a bandwidth of 400 has the half-power points at 300Hz and 500Hz." With a bandwidth of 400, the difference between the lower and upper cutoff frequencies is 400, so if we think of it linearly (which is not correct, but simple and intuitive), the lower cutoff would be 200 and the upper cutoff 600. As we are working with logarithmic representation, I think the numbers would be more like approx 240 and 640. Others here will know with better mathematical precision ;-) There is a quite clear explanation of filter bandwidth formulas on this page https://www.ranecommercial.com/legacy/note170.html I keep coming back to that resource all best Øyvind lør. 14. des. 2024 kl. 01:24 skrev Jeanette C. <julien@mail.upb.de>: Hey hey, I am just experimenting with multiband stuff. I try to split a signal into three or four bands. The lowest band uses a lowpass filter and the highest a ighpass filter. In between there should be one or two bandpass filters. I have started work with Butterworth filters. I try to filter the signal so, that the outputs of the filters, taken together, (nearly) reconstruct the original signal. I am not set on the Butterworth filters and the crossing points in the setup below, can be purely nominal. They don't actually have to represent a frequency of one of the filters, if it makes all the calculations easier. So, I have some issues with half-power points. Here's my current setup, with a few hardcoded values. iCross1 init 200 ; nominal lowpass frequency iCross2 init 800 ; nominal highpass frequency iCentre init (iCross1 + iCross2) / 2 ; the mid-point between the two iBandwidth init (iCross2 - iCross1) * 2 ; The bandwidth The output sounds not too bad. But there are issues. A bandwidth of 1200 with a centre of 500 would result in a negative frequency for the lower "edge" of teh bandpass filter. I was working from the following, possibly wrong or misunderstood, example: a second-order Butterworth Bandpass filter centred at 400Hz with a bandwidth of 400 has the half-power points at 300Hz and 500Hz. So I'd assume that it would have the half-power points at 200Hz and 600Hz with a bandwidth of 800. Can anyone suggest a better approach or point out my wooly thinking, please? Best wishes, Jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c There's no time to loose And next week, You might not see me here <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here

Date	2024-12-14 13:43
From	Lovre Bogdanić
Subject	Re: [Csnd] Butterworth filters and signal splitting
	This is one nice and helpful library for filter design: https://github.com/chipmuenk/pyfda You don't need to know python to use it, you just need to install it. You do everything using GUI Steps typically are that you specify the type of filter you want (LP, HP, BP ...), choose implementation FIR or IIR (Butterworth among others), define filter order and wanted frequencies and the tool will then show you filter characteristics and calculate filter coefficients for you. Then you can use those coefficients with filter2 opcode (https://csound.com/manual/filter2.html). I haven't used filter2 but I think it will do the trick. Best, Lovre On Sat, Dec 14, 2024 at 1:42 PM Oeyvind Brandtsegg <obrandts@gmail.com> wrote: Hi Jeanette, It looks like your estimation of crossover frequencies are off (or at least different than what I think). You write "a second-order Butterworth Bandpass filter centred at 400Hz with a bandwidth of 400 has the half-power points at 300Hz and 500Hz." With a bandwidth of 400, the difference between the lower and upper cutoff frequencies is 400, so if we think of it linearly (which is not correct, but simple and intuitive), the lower cutoff would be 200 and the upper cutoff 600. As we are working with logarithmic representation, I think the numbers would be more like approx 240 and 640. Others here will know with better mathematical precision ;-) There is a quite clear explanation of filter bandwidth formulas on this page https://www.ranecommercial.com/legacy/note170.html I keep coming back to that resource all best Øyvind lør. 14. des. 2024 kl. 01:24 skrev Jeanette C. <julien@mail.upb.de>: Hey hey, I am just experimenting with multiband stuff. I try to split a signal into three or four bands. The lowest band uses a lowpass filter and the highest a ighpass filter. In between there should be one or two bandpass filters. I have started work with Butterworth filters. I try to filter the signal so, that the outputs of the filters, taken together, (nearly) reconstruct the original signal. I am not set on the Butterworth filters and the crossing points in the setup below, can be purely nominal. They don't actually have to represent a frequency of one of the filters, if it makes all the calculations easier. So, I have some issues with half-power points. Here's my current setup, with a few hardcoded values. iCross1 init 200 ; nominal lowpass frequency iCross2 init 800 ; nominal highpass frequency iCentre init (iCross1 + iCross2) / 2 ; the mid-point between the two iBandwidth init (iCross2 - iCross1) * 2 ; The bandwidth The output sounds not too bad. But there are issues. A bandwidth of 1200 with a centre of 500 would result in a negative frequency for the lower "edge" of teh bandpass filter. I was working from the following, possibly wrong or misunderstood, example: a second-order Butterworth Bandpass filter centred at 400Hz with a bandwidth of 400 has the half-power points at 300Hz and 500Hz. So I'd assume that it would have the half-power points at 200Hz and 600Hz with a bandwidth of 800. Can anyone suggest a better approach or point out my wooly thinking, please? Best wishes, Jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c There's no time to loose And next week, You might not see me here <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here

Date	2024-12-14 14:18
From	"Jeanette C."
Subject	Re: [Csnd] Butterworth filters and signal splitting
	Hi Lovre, Dec 14 2024, Lovre Bogdanić has written: > This is one nice and helpful library for filter design: > https://github.com/chipmuenk/pyfda ... Do you know if this tool works completely without a GUI too? If not, I can always check, but it will take a little more time. :) Thanks anyway for stepping in and suggesting that tool. Best wishes, Jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c Skip on the drinks Head to the floor Makin' my way Past the show My body's taken over And I want some more <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here

Date	2024-12-14 14:39
From	"Jeanette C."
Subject	Re: [Csnd] Butterworth filters and signal splitting
	Hi Oeyvind, many thanks for sharing that resource. The article seems quite conciise. Alas, the formulas are all in images. But it's a nice start. Best wishes, Jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c Skip on the drinks Head to the floor Makin' my way Past the show My body's taken over And I want some more <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here

Date	2024-12-14 18:10
From	"Jeanette C."
Subject	Re: [Csnd] Butterworth filters and signal splitting
	Hey hey, here's a demo version of the idea with two instruments, one for simple usage, the other for more creative usage: https://www.dropbox.com/scl/fi/lypivjdcp2o2ndnkk07cr/m_ws_fork.csd?rlkey=k87k1885x1tn9yijjqbx9isiy If you have further pointers to improve the crossover between the bands, please let me know. Best wishes, jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c Don't worry, you're gonna be alright, But Cinderella's got to go <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here

Date	2024-12-14 22:25
From	"Dr. Richard Boulanger"
Subject	Re: [Csnd] Butterworth filters and signal splitting
	jeanette, nice! thanks for sharing. - Dr.B Dr. Richard Boulanger Professor Electronic Production and Design Berklee College of Music Professional Writing & Technology Division On Sat, Dec 14, 2024 at 1:10 PM Jeanette C. <julien@mail.upb.de> wrote: Hey hey, here's a demo version of the idea with two instruments, one for simple usage, the other for more creative usage: https://www.dropbox.com/scl/fi/lypivjdcp2o2ndnkk07cr/m_ws_fork.csd?rlkey=k87k1885x1tn9yijjqbx9isiy If you have further pointers to improve the crossover between the bands, please let me know. Best wishes, jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c Don't worry, you're gonna be alright, But Cinderella's got to go <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here

Date	2024-12-14 23:17
From	"Jeanette C."
Subject	Re: [Csnd] Butterworth filters and signal splitting
	Hello Richard! Dec 14 2024, Dr. Richard Boulanger has written: > jeanette, > > nice! thanks for sharing. Thanks for the feedback. I wasn't sure if this is really ready and I might add more functionality. It was inspired by the Befaco Bandit module: https://shop.befaco.org/Assembled/1330-bandit-assembled-module.html DivKid has also done a nice Youtube video on that: https://youtu.be/ExeBPLxMV2o In that respect my code lacks quite a few features. :) -- Well, this code will shortly disappear. I think I'll leave it there till tomorrow night or so. Best wishes, jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c Don't worry, you're gonna be alright, But Cinderella's got to go <3 (Britney Spears) Csound mailing list Csound@listserv.heanet.ie https://listserv.heanet.ie/cgi-bin/wa?A0=CSOUND Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here