Can we borrow/repurpose you’d BBD line and so forth Surge?

[baconpaul]

Hi @jpcima

Hope all is well

One of our users suggested that we add an emsemble chorus to Surge and another pointed at this code. Would you be OK if we used some of this code directly and indirectly to add a modified ensemble chorus to Surge, crediting you in the changelog and everything of course.

Boost license would let us do it without asking, I guess, but thought asking would be polite!

Let me know if that’s OK and we may add it to our book of work!

[baconpaul]

Oh just looking you link to https://colinraffel.com/software/bbdmodeling/echo.cpp which is super handy too!

[jpcima]

Hi @baconpaul

You're free to use any work around this as you see fit.
However this software is not the best reference of how to implement it.
I based it on some missing/outdated info and guesses back then, not real knowledge of the circuit, and this plugin is incorrect and due for a huge rework.

I can point you to some better resources

• We have an emulation of Roland BBD chorus which is correct wrt the circuit.
  It implements a virtual BBD off a dafx 2019 paper which is more recent than C. Raffel's
  Also has a custom-made stereo variant
  https://github.com/jpcima/rc-effect-playground
• Chenille user manual. Has block diagram of system for how to combine up to 6 BBD lines, and lists phase offsets of some known hardware. Probably it's not too hard to derive such a system from existing work above.
  http://jiggery-pokery.com/jp_re/chenille.html
• A Solina variant in source code of String-machine
  https://github.com/jpcima/string-machine
• J. Haible Triple Chorus technical notes http://jhaible.com/legacy/triple_chorus/triple_chorus.html
  Quickly judging by @mkruselj 's comment, I think he has it correct BBD ensemble/chorus surge-synthesizer/surge#3743 (comment)

At your service if I can provide any useful infos :)

[jpcima]

Addendum There's also a Huovilanen simplistic BBD model in this paper. I've not tried it or compared.
(because computing bbd multi-rate is not always cheap, especially at slow clock)
http://www.dafx.de/paper-archive/2005/P_155.pdf

[mkruselj]

http://jhaible.com/legacy/triple_chorus/triple_chorus.html

@baconpaul This is an excellent description of the inner workings! Should help us get to where we want completely.

[baconpaul]

Oh awesome thanks @jpcima

[baconpaul]

And yeah the BBD line in your string machine code looks great. That 2005 paper also super clever but from here I bet we can adapt to surge - thank you very much!