Feedback is Everywhere

Words by Knut Aufermann

14

About 12 years ago I was taking part in a work placement at a governmental Institute for Chemical Analysis in Hagen, Germany. One day my supervisor did not have much work to do so he showed me a book he found called ‘Chemical Show Experiments’1. After a quick flick through it we decided to try the ‘Chemical Clock’. Four different substances are mixed together in a big glass cylinder and then stirred constantly with a motor. Nothing seemed to happen at first but after about one minute all of the clear liquid instantly turned pitch black. Then clear again and then black again with frightening precision. Every few seconds this chemical clock would change its colour and this process went on for more than an hour. This reaction was also called a ‘Chemical Heart’ and it felt quite alive to me.

Going back to school I questioned my chemistry teacher about this experience. Having learned that the laws of thermodynamics say that every reaction strives towards an equilibrium this chemical clock did not make sense. My teacher told me that it was very close to its equilibrium, just with tiny disturbances before it settled down completely, and that the change of colour fell by chance into this near-equilibrium area.

A few years later I read the book Order Out Of Chaos by chemistry Nobel Prize winner Ilya Prigogine and Isabelle Stengers, and discovered that the chemical clock was called the Belousov-Zhabotinsky reaction and that my school teacher was wrong. Chemical reactions can be stable or oscillate far away from equilibrium, in fact most of the functions in cell biology rely on this behaviour.

Several years after that I found myself trying to learn how to operate a NEVE VR mixing console with flying faders. Impressed by the amount of buttons to press I lost track of my actions and at a flick of a switch created an internal electronic feedback loop. All meters showed me their red LED’s and the speakers created a spectrally rich, wonderfully loud roar. An alerted staff member opened the sound proof door and asked if I was okay.

Nowadays I deliberately use internal feedback between electronic equipment to produce sounds. At a recent visit to a library I stumbled across the book by Prigogine and Stengers again and reread the chapter on the Chemical Clock. This time the underlying reaction mechanism (called autocatalysis: X supports the production of X in the simplest case) became clear: the existence of a feedback loop throws the system into an oscillating behaviour far away from its equilibrium. Now this statement is equally valid for my sound set-up. The same concept lies behind a show experiment of inorganic chemistry and the sound which emerges from wrongly connected effects units. So why is this whole thing so interesting?

For me it is the behaviour of the system. Both the Chemical Clock and feedback sounds are mesmerising. And it gets even more interesting when you can play with it. The complex quality of the (un)predictability of my feedback sound set-up is a constant challenge. For a closer description of these qualities I like to employ the following analogy: What would my feedback instrumentarium behave like if it were a piano?

My fascination when performing live is the limited but nevertheless existent predictability that forces the player to use intuition instead of technical skill, anticipation instead of predetermination — all in the knowledge that tiny changes can have huge effects and that you have to accept what you get.

In my search for more relationships between feedback sound and science I came across a computer program that creates sonograms. These are displays of the frequency range over time (with the amplitude of the frequency shown by the shading) of a sound file that is analysed using the mathematical method of Fast Fourier Transformation (FFT).

15

Sonogram of the first six seconds of Track 2 of the Resonance CD. Horizontal axis: time. Vertical axis: frequency

The sonograms shown here were taken from a live track (an excerpt of which you can find on Track 2 of the accompanying CD). They show stable and unstable oscillations, emerging patterns of different complexity (and beauty), chaos and the existence of continuous and discrete, quantised spectra of frequencies. Given the correlation between energy and frequency (E=hv) stated by Einstein and De Broglie one could compare these sonograms with findings from quantum physics. Some tones produced through feedback show quantised energy levels throughout the audible range. Perhaps these analogies are a bit far fetched, but the dilution of the strict separation between actor and spectator during experiments as proclaimed by quantum physics — and thus the possibility of a constant feedback loop between experiment and experimentalist — is a lot like the relationship between feedback players and their instruments.

In general this necessity of a feedback loop applies to all forms of communication. It is the case for communication between players in musical improvisation just as it is between the billions of molecules which change colour at the same time in the Chemical Clock. Feedback processes are everywhere.

I would like to close the circle with another story from the chemistry world told by one of my former professors. As a student he found himself out of money and out of fuel for his car. Applying his chemical knowledge he went to his lab, stole a bottle of pure octanol (with a possible octane count of 100) and filled his car’s fuel tank. It was only after he had managed to drive all the way to his house that he realised the engine would not stop after he took out the key. Without being able to stop the fuel flowing he had to leave his car running in front of his house until the tank was empty. Surely the motor was engaged in some sort of feedback reaction.

 

SOURCES

  1. Prigogine, I. & I. Stengers, Order Out Of ChoosMan’s new dialogue with nature (London: Fontana, 1985).