A little dab

May 31, 2021
 by Paul McGowan

In 2008, authors Karl Johan Åström and Richard M.Murray wrote about feedback: "Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole."

Now, that's about as nerdy as one can get but their point is well taken. One must look at the whole.

Feedback is taking the outcome of a past event and, in the future, comparing it to one's original expectations.

We have many different forms of feedback: from customers, friends, family, our own internal loops.

In circuits there's also a great variety: loop, local, forward, negative, positive.

In my experience, the best use of feedback is to have it do as little as possible. In other words, we shouldn't rely upon feedback to set our course. Rather, feedback should be the finishing touch.

This applies equally to personal and company feedback as well as circuits. We know that if an audio amplifier's open-loop performance (operation without feedback) is good, then the addition of feedback generally makes things sound better. We also recognize that the opposite is true. Rely upon feedback for an amplifier's stable operation and the audible results are not worth your time.

Like all things in life, a little dab'll do ya'.

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20 comments on “A little dab”

  1. These days I need a rug before the 'Brylcreem' will have any use at all on my noggin 🙁

    HEGEL appears to be having immense success with
    their analog computer 'Feed Forward' topology.

        1. Yes, welcome to the 'can comb your hair with a hot dog' club.
          And remember, the term "hair" can be both singular OR plural..

          I remember a bazillion years ago - I thought I'm gonna be a big boy & brush my teeth all by myself without being instructed to do so - to the biffy I went, opened the drawer and grabbed my brush & the tube and put a DAB of Brylcreem right into my micro-toothed yap.. I got about half a dozen strokes in before the burning began. One of my first childhood memories... That sh1t is NOT minty fresh!

  2. This post was fed through, analyzed and looped around the old cranium.

    Nice post Paul. I’ve been enjoying your more philosophical pondering lately. 🙂

    1. Mind if I chime in. This is a really great post Paul. Maybe some other designers will start finally get the point of feedback used properly.

  3. Paul, you’re showing our age. Next, you’ll be referencing either the Burma Shave or the Bosco commercial. Leaving on a musical note, Circus Boy and Michael Nesmith are having their farewell tour later this year. Will their last song be "hey hey we’re the Monkees"?

  4. In my professional career I hated "partnering" and endless client and public feedback, but it was a necessary evil, especially on projects involving many agencies and user groups. Yes, most feedback was idiotic and counterproductive--a waste of time and resources. But sometimes feedback exposed a problem that if recognized too late would have required very costly backtracking to correct. One project involved 50 public presentations, hundreds of agency meetings and the addressing of thousands of review comments. We spent more time responding to feedback than actual design and engineering. Soliciting feedback was part of getting the "buy in" of parties who could create real problems for us down the road. Get them involved early and make them feel like part of the design process, even if they contribute nothing. LOL

  5. I take it from this and other recent posts that PS Audio is not developing a proprietary ultra-low noise, low distortion, super-efficient and low cost switch mode power supply.

  6. Feedback was invented by a Bell labs scientest to clean up long distance voice transmission in the early days. The bandwidth of that sound was quite narrow. Fidelity was not primary. Clarity was. The same man developed feed forward but preferred feedback since it was much simpler to implement. But it's always seemed that feed forward could be more time coherent than feedback and it's the potential 'long' time lag in feedback that causes its problems.

  7. THX AAA feed forward invention provides zero point as many as you like zeros distortion.
    It is implemented in the new well-reviewed Benchmark power amp.
    If everyone uses it, all amplifiers will sound the same, won’t they.

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