You are probably already using Zero Delay Feedback filters, so let your customers know!

[andy-cytomic]

I thought it might be useful for people to know that for anyone using RBJ audio eq cookbook code (or any other bilinear z transform method) these are in fact Zero Delay Feedback filters! That's right, anything that uses trapezoidal integration, which is an implicit integration method, solves for things without any delays in feedbacks

So now you can all in good conscience, and with complete honesty, add the wonderfully enticing bullet point to your feature list:

• Featuring Zero Delay Feedback technology!

[EvilDragon]

[whyterabbyt]

Wow. My old plugins suddenly sound better!

[adrien59cadri]

Hello

Arturia TAE in particular has been using even more than this for years and never branded a ZDF feature.

Best

[jupiter8]

Fail. Analog filters do have delay,it's the law of physics. Actual Analog Emulation is 0.000001 delay filters. I rule.

[FabienTDR]

Fail. Analog filters do have delay,it's the law of physics. Actual Analog Emulation is 0.000001 delay filters. I rule.

I don't like the term either (it's as confusing as it can get). But I think the original and heavily misunderstood paper means


"Zero-Delay-Feedback filters"

and definitely not

"Zero-Delay Feedback-Filters"

However, the latter is what the typical, uneducated plug-in user thinks when he hears the term... That's exactly how advertscience should be: Easy to confuse.

[mystran]

I always liked the label "topology preserving" a bit more, as it sort of emphasizes that it's not about the transfer functions but rather about what kind of topology you have. But even that's a bit silly, because really all you need is to integrate a DAE one way or another and if it's LTI then even a direct form is perfectly valid way to solve it (well, at least in exact arithmetics, but that's another thing).

[Urs]

I can't resist to say, as DF1 filters do not sport a representation of any feedback path of an analogue circuit, they quite clearly can't feature it

(I wonder though whether or not the German term "Den Teufel durch Beelzebub austreiben" - fight one evil with another - applies here)

[Z1202]

I thought it might be useful for people to know that for anyone using RBJ audio eq cookbook code (or any other bilinear z transform method) these are in fact Zero Delay Feedback filters! That's right, anything that uses trapezoidal integration, which is an implicit integration method, solves for things without any delays in feedbacks

So now you can all in good conscience, and with complete honesty, add the wonderfully enticing bullet point to your feature list:

• Featuring Zero Delay Feedback technology!

I would say this is simply plain wrong. Trapezoidal integration implies bilinear transform, but not the other way round.

PS. Andy, don't you think you're going a little bit too far in trying to prove that the TPT method contains no novelty whatsoever? Well, up to you, man...

[xoxos]

0dff has been immaterial since *exactly* the point in time when *i* was able to offer them.

tune into your frankenstien earphone radio headset with all the deadly worldwide computer god gangster controls, and you'll know it's *exactly* true.

hth, and thanks

[Z1202]

This is more or less my public reply to Andy (frankly speaking, I get a little bit tired of his reiterating attacks), as to my position of the novelty of TPT (which others prefer to refer to as ZDF).

As for the novelty of the method itself, TPT is a combination of block-diagrams, trapezoidal integrator replacement and zero-delay feedback, all three done simultaneously. I never claimed to have invented any of those separately (okay, I have reinvented the ZDF part, but I never claimed it as my invention). However, I would still like Andy to point me to an earlier piece of art using those three simultaneously for the purpose of building a VA filter model. If he does this, I will publicly admit the priority of that person's invention.

As to this combination presumably being self-obvious, I'd like to remind Andy that not only this combination hasn't been widely known (if existed at all), but on the opposite, most prominent VA works, like the ones of Huovilainen, IIRC, were exclusively limited to explicit integration schemes, and also quite a number of works in the VA field were concerned with fixing the problems of DF forms or Chamberlin SVF, whereas those problems would be immediately gone in the TPT approach. The majority of the music DSP community has been stuck with explicit methods for what reason ever.

As to being equivalent to the trapezoidal integration of the differential equations. Yes it is. But two equivalent methodologies are still two different ones. In this regard I particularly wonder, if avoiding of doubling of the number of state variables in the trapezoidal integration method (which IIRC was one of the subjects of Andy's "optimized" trapezoidal SVF and which is given for granted in TPT) has been known before?

Edit: as to original Andy's claim in this thread, I think the correct way to phrase it would be "if your plugin's filters are made by trapezoidal integration, then you can claim that it has ZDF". But don't be lured into a trap of thinking that bilinear transform automatically means trapezoidal integration or ZDF. If that were the case, the TPT (or ZDF) approach would have offered no improvement whatsoever over the direct forms.

[Z1202]

BTW, it just came to me, that if we take Andy's approach of judging novelty, then we should say that Antti Houvilainen didn't introduce anything new with his Moog filter model at all. Indeed, Ebers-Moll transistor model, basic laws of electricity and Euler method are nothing new at all. And Antti simply applied them to the schemantics of the Moog filter. What should be novel at that? So, come on, Andy, tell us that also Antti didn't invent anything!

Well, in my point, the novel, nontrivial and most valuable aspect of Antti's work was that he realized that these (trivial by themselves) steps are worth doing, because then you will get a better digital model than the previously existing ones. In a similar fashion, I believe that my contribution was in realizing that you can combine the bilinear transform and topology preservation into one approach, zero-delay feedback serving as a glue. Apparently a similar realization was made earlier by Serafini and others for the trapezoidal integration approach (which for whatever reason remained unknown for a large if not major part of the music DSP society), but that's IMHO a different, although mathematically equivalent, method.

[andy-cytomic]

I thought it might be useful for people to know that for anyone using RBJ audio eq cookbook code (or any other bilinear z transform method) these are in fact Zero Delay Feedback filters! That's right, anything that uses trapezoidal integration, which is an implicit integration method, solves for things without any delays in feedbacks

So now you can all in good conscience, and with complete honesty, add the wonderfully enticing bullet point to your feature list:

• Featuring Zero Delay Feedback technology!

Actually it gets better, I just realised that the bullet point above you can actually apply to the following circuit:




So anywhere in your code you have an assignment operation you can also quite literally say you are using Zero Delay Feedback technology, yippeee!

[andy-cytomic]

I can't resist to say, as DF1 filters do not sport a representation of any feedback path of an analogue circuit, they quite clearly can't feature it

(I wonder though whether or not the German term "Den Teufel durch Beelzebub austreiben" - fight one evil with another - applies here)

But they do. Take the laplace transform of an SVF to get your s domain biquad, then realise this circuit with feedback in a time invariant way using the bilinear transform with a DF1, and your zero delay feedback is modelled, yaaa!!!

[andy-cytomic]

Fail. Analog filters do have delay,it's the law of physics. Actual Analog Emulation is 0.000001 delay filters. I rule.

Filters delay, but here we are talking specifically about if there is any delay included in the model of feedback paths of the circuit.