I'm probably tempting fate since a lot of this is Greek to me, but ...hakey wrote:What I meant was that a system in which the output is fed back into the input is nonlinear, and that's what's happening with the 0df filter, no?xh3rv wrote:Technically I don't think 0df *has* to model nonlinearities, but it's very different in theory and computation from moving the non-linearities inside the feedback loop as necessary to model analog hardware.
Feedback is nonlinear.
Vadim Zavalishin's The Art of VA Filter Design includes a section on a zero delay feedback filter with no non-linearities at the end of chapter 3. There is some variance and nuance in what 'linear' means between filter design versus some other scientific or mathematical contexts, and I can't quite formulate but sort of get the sensibility that feedback is non-linear. But sticking to convention, I think this is strong evidence. Interestingly Vadim notes a 'smoothing' element should be in place in his linear 0df example, and later in ladder & diode chapters uses non-linearities as an alternative - I think this is where the mojo happens, it's really complex, chaotic behavior here.
(Link to Vadim's text) http://ay-kedi.narod2.ru/VAFilterDesign.pdf
