Talk:Feedback

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is external linking allowed?, in any case much good info in http://prof.usb.ve/williamc/Mejoramiento/historia.html should be made available here

in electronics the para are disordered, positive feedback (suject of great Armstrong deForset patent dispute)predates Black's negative feedback amplifier and should be refered to first, PID is a subset of negative feedback control techniques :jcox

--- I don't believe that the explanation of audio feedback is correct. It identifies the frequency of feedback noise as related to the transit time through the system (Implying it's a matter of repeating the waveform, the effect you might get with digital echo or flange). But I'm 95% sure that's completely irrelevant in a system like this, the waveform is completely obliterated by all the transitions made, all you're left with is frequencies that approximate those you started with.

OK, a quick test: I was able to get audible feedback with a 1/2 second delay in the loop, which should give a frequency of 2 hz, 5 octaves below audible.

So I'm rather sure the frequency of feedback is not determined by transit time, but by the frequency response of the whole system. All real world systems contain some capacitance and inductance, meaning they all act as very wide, low, bandpass filters. But when you amplify and feedback the filtered sound into the filtered sound, you've naturally created an oscillator (the simplest forms of analog oscillators work on exactly this principle).

So unless anyone objects I'm going to change the explanation to reflect this. User:Wji

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Although feedback was perhaps discovered during the course of the development of electronics, it exists in many natural processes and the word (although not present in earlier dictionaries, for example the original OED) represents a concept in general use outside engineering. Therefore the article should begin with the general concept but include a substantial section on control theory. I was first introduced to feedback during training on servo mechanisms many years ago and am a bit rusty, but I clearly remember it took both positive and negative feedback to make them work. What we call feedback like with a microphone is perhaps not feedback in the sense we are using it here. User:Fredbauder

I agree that there is more than one sense of the word feedback. The Penguin Dictionary of Electronics, for example, has separate entries for feedback in the general sense and feedback control loop in the specific context of control systems. The Chambers Science and Technology Dictionary has headings for feedback (acoustic), feedback (telecommunications) and feedback control loop, so perhaps there are really three different concepts. If we wish to separate the general from the particular, I would suggest the following structure for the Wikipedia (with separate articles for hunting and feedback):

• Hunting (known to mechanical engineers as early as 1880, according to OED2)
• Feedback
  • as originally defined, i.e. in electronic amplifiers (see OED2 citation from 1920)
    • acoustic feedback in public address amplifiers (OED2 has a 1921 citation of howl) - perhaps this could be a separate article
  • feedback theory applied to control loops (probably first applied in World War II)
    • control loops in nature, i.e. natural systems that can be analysed with control loop theory (existing since prehistory but only understood by humans in the light of control theory)

Do you think this is reasonable? Unfortunately it contradicts your idea of putting the natural phenomena first. My scheme lists things in the order of discovery by man, whereas yours is nature-based. I cannot say which is better.

As for the microphone example, this is an illustration of feedback in the electronic (or electroacoustic) sense, not in the control loop sense. The feedback is always positive, because sound from the loudspeakers is always added to, never subtracted from, the sound entering the microphone. What changes is the loop gain, which varies as the user moves the microphone relative to the speakers. As soon as the loop gain exceeds unity, the system howls. This effect is independent of frequency. I believe that a system with negative feedback can only become unstable if the signal frequency exceeds the bandwidth of the feedback loop.

In control theory you can have multiple feedback paths (often three: proportional, integral and derivative) and it is meaningless to talk about overall positive or negative feedback, because the three paths may have different characteristics. --Heron

What I suggest is a simple introduction which includes the general case, followed by as much specialized technical information as you feel appropriate. I agree the notion of postive and negative is applicable only to 2 dimensional systems, but I think it should remain in the introduction. I don't think organization around order of discovery is good; I prefer organization to start with a brief general introduction using simple language and concepts followed by (in this case) an engineering section, followed by the ways the concept has been adapted to natural systems. I guess runaway positive feedback is what we are talking about with apmplifiers. Fred Bauder

I divided the article into sections, without changing the words much. I may go further and remove the acoustic example to a separate article, but I'll leave 'hunting' where it is. --Heron

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I have been bold and removed the acoustic feedback section totally. I have linked the existing article at Audio feedback to the disambiguation page. The main differences in the removed section (reproduced below) lacking in the original page are the points about the band-pass filter and the electronic oscillator.

I believe the band-pass filter point is incorrect anyway. True, all systems have some kind low and high pass filter in them, but this is generally well outside the human range of hearing, and in any case, makes no difference to the presence of feedback. The deleted section was also vague as to whether this was affecting the presence or nature of the feedback, but if it were just the latter, there are plenty of other factors involved (at the very least, the inherant EQ of the system would be much more important).

Also, the electronic oscillator point seems slightly amibiguous too, although I could understand if people wanted this link in the main article. It might be worth pointing out that the simplicity is certainly not in the waveform, but in the construction. --postglock 07:49, 6 Jun 2005 (UTC)

Feedback in audio systems

Main article: Audio feedback.

A well-known example of runaway positive feedback in electronic systems is called "howl" or "howl-round". This occurs in public address systems when sound from the loudspeakers reaches the microphone, is amplified by the system, and is then fed back into the system at even higher volume. All electrical systems contain capacitance and inductance and so act as band-pass filters responding better to certain frequencies. In a single loop through the system, this effect is negligible, but it becomes severe when the signal passes through the system repeatedly. This effect is the basis of the simplest kinds of analogue electronic oscillator.

on mention of "audio feedback"at top

postglock- lemme know if my last version works for you. thankz, Ished-out amounts of Vonn-ness 14:19, 10 September 2005 (UTC)

Problems with the current definition of "Feedback"

> Feedback is the signal that is looped back to control a system within itself.

I am troubled by this definition. Over the next few days I'll seek sources to back up my concerns and add to this comment when I find them. But in the mean time, here's some food for thought.

Consider Jimi. I suspect that some (not me) might term his explorations of feedback as pure noise. :) More formally, the word "signal" is often used in information theoretic contexts as something distinct from noise. I would argue that an elimination of the distinction between signal and noise, a priori, is central to how order emerges from chaos. In summary, I question use of the word "signal". Similarly, the words "control", "system", etc. seem to demand that order is involved a priori, and, as a consequence, to prematurely evoke a teleological perspective.

What is your favorite, least constraining definition of feedback?

love, raiph 03:44, 3 October 2006 (UTC)

Proposal to refactor content

There's a long laundry list of important theories, phenomena and more built directly on top of feedback loops that aren't mentioned on this page but should, imo, be considered. (I think I could easily list a dozen, and maybe a hundred, but the specifics aren't my point and I really don't want to get into that game yet if we can avoid it.)

Conversely, much of what's on the page right now seems too detailed, even for me, someone who's been intellectually focused on feedback loops for over a decade.

I propose I/we refactor the page. The introduction should be as general as possible. A History section seems a natural. Maybe an Examples section. I see most of the details of particular feedback phenomena going on their own pages.

Comments?

love, raiph 03:44, 3 October 2006 (UTC)