You may have witnessed feedback in a concert or when your speaker output in a live chat feeds back into your microphone input. A high pitched noise slowly gets louder, then raises exponentially until someone pulls the plug and suddenly a breakdown of signal strength occurs.

You have experienced a bubble.

Being a designer of digital filters, I want to raise awareness of how destructive these bubbles may be to democracy and diversity of opinions - contributing to instability and irrationality.

Stockmarkets, search ranking algos, facebook likes, reddit/mastodon upvoting, opinion polls, “news” in general - all have their respective feedback channels built in.

Feedback is established when past voting results (or price feeds) are visible to those voting in the future.

This may seem benign. It is not. It creates a exponential response. It risks getting chaotic and tends toward bifurcations/splitting. The complexity of not one but many such feedback channels will be explored next.

  • itsmectEnglish
    3·
    9 months ago

    For the uninitiated: In signal processing, feedback is not a good or bad thing, but a fundamental building block.

    • Any modern power supply works by measuring its output voltage and compares it to a reference. If its to low, it increases the output voltage; if its to high it decreases the output voltage. This so called negative feedback loop compensates the error.
    • Now what happens if the system reacts to slow? If the system thinks the output voltage is to low, it keeps increasing the output voltage, even if it has already recovered. Once it reacts to the high voltage, it already overshot the set point, tires to course correct, but undershoots this time, causing an oscillation.
    • If each over/undershoot decreases compared to the last one, the oscillation will decay. If it happens in a short time, it is often not a huge issue. This is called a stable system.
    • If each over/undershoot is identical compared to the last one, the oscillation will continue. This is also useful, and utilized in all of out clocks. This is called an marginally stable system.
    • If each over/undershoot increases over time, the oscillation will increase until the output physically can’t go any lower or higher. Unsurprisingly this is called an unstable system. In some systems the connected electronics may not tolerate such high voltages and break, which must be avoided at the design stage.

    Why am I telling you this? Because humans and society as a whole reacts to their environment slower than the environment changes, making us all effectively a shitty feedback system (what this post is about). The oscillations can eg. be observed in the economy as Recession/Growth cycles. When money gets printed, invested and burned the oscillations get another “push” and keep going. Well until they hit their physical limit eventually, which will be quite dramatic.

    Generally Recession/Growth cycles are treated as given, a natural cycle like summer and winter. But I don’t think they are. They are the result of us not understanding the root causes, not bothering to fix them or simply being not able to. Except now we have money with a constant linear emission rate, which results in decreasing relative changes, which in turn is an ideal mathematical function to dampen a oscillating system.

    • hfondOPMEnglish
      2·
      9 months ago

      Welcome. I thought of constructive use cases, after all my own designs are supposed to be stable. You mention impulse response and time constants - but for now I want to address a broader public.

      I want to raise awareness of the ways feedback is managed in undemocratic ways. Insider: D. Farmer said: "It is (so called) risk management that causes instability in these markets " The crucial question is that of foreknowledge, or, in dsp terms feed foreward paths, or, in finance moral hazard aka foreknowledge that big boyz can avoid responsibity. I’ll leave that for later, too.

      Have a nice one.