>rbj >it's a technical fact in a causal environment. y[n] is a function of y[n-1], y[n-2]... and x[n], x[n-1], x[n-2] ...
True as stated, but nothing there prevents anybody from defining y[n] implicitly (i.e., as a function of the above *and* of y[n] itself). Indeed, for some systems there is not going to be any equivalent algebraic expression for y[n] purely in terms of previous y[n]'s and previous/current x[n]'s. So this seems to be more or less a semantic issue. Personally, I am fine with the term "zero-delay feedback." An iterative solver applied to an implicit equation seems like a pretty reasonable approximation of the physical systems in question, wherein feedback paths are connected without any explicit delay elements in them. I imagine the iterations as corresponding to successive propagations of voltage/current through the feedback path (of course these happen very quickly in the analogue case, and the system never "holds still" at any point like in a digital simulation, but you get the overall idea). We could issue the same objection to analyzing feedback paths in analogue circuits as "zero-delay," (since it always takes electricity some finite time to propagate around the path) but it wouldn't make the zero-delay approximation and associated fixed-point characterizations any less useful or accurate. What's the point? E On Tue, Jun 24, 2014 at 8:37 AM, robert bristow-johnson < [email protected]> wrote: > On 6/24/14 6:00 AM, Urs Heckmann wrote: > >> You're right. >> >> I've been worked up ever since people post those silly and ignorant stabs >> like this: >> >> On 09.04.2014, at 19:12, robert bristow-johnson<[email protected]> >> wrote: >> >> if there is feedback, there must be at least one sample of delay, >>> despite claims of zero-delay feedback i have read here on music-dsp and at >>> other places. >>> >> > it's a technical fact in a causal environment. y[n] is a function of > y[n-1], y[n-2]... and x[n], x[n-1], x[n-2] ... > > what's the next claim we'll be hearing about? that we can get feedback of > -1 or -2 samples "delay"? why not? it's just more extrapolation. > > > It occurrs that the topic triggers an immense resistance with those who >> have stakes in DF-anything. >> > > i never brought up DF-anything in this thread. i *did* respond to it a > little bit (mostly just to direct the discussion back to the topic). i > regret that i responded to it. this thread has nothing to do with > DF-anything. > > > It occurrs that no proof is enough to stop those people from stabbing. >> > > "no proof" is what we're seeing. > > > Therefore I see no benefit in discussing the topic any further. >> >> > it's one way to settle an unsupported claim. > > > -- > > r b-j [email protected] > > "Imagination is more important than knowledge." > > > > -- > dupswapdrop -- the music-dsp mailing list and website: > subscription info, FAQ, source code archive, list archive, book reviews, > dsp links > http://music.columbia.edu/cmc/music-dsp > http://music.columbia.edu/mailman/listinfo/music-dsp > -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp
