The Brain Making Sense of an Orchestra

But our unconscious feats of unweaving and weaving are greater even than this. Think what is happening when you listen to a whole orchestra. Imagine that, superimposed on a hundred instruments, your neighbour in the concert is whispering learned music criticism in your ear, others are coughing and, lamentably, somebody behind you is rustling a chocolate wrapper. All these sounds, simultaneously, are vibrating your eardrum and they are summed into a single, very complicated wriggling wave of pressure change. We know it is one wave because a full orchestra, and all the noises off, can be rendered into a single wavy groove on a phonograph disc, or a single fluctuating trace of magnetic substance on a tape. The entire set of vibrations sums up into a single wiggly line on the graph of air pressure against time, as recorded by your eardrum. Mirabile dictu, the brain manages to sort out the rustling from the whispering, the coughing from the door banging, the instruments of the orchestra from each other. Such a feat of unweaving and re-weaving, or analysis and synthesis, is almost beyond belief, but we all do it effortlessly and without thinking. Bats are even more impressive, analysing stuttering volleys of echoes to build up, in their brains, detailed and fast-changing three-dimensional images of the world through -which they fly, including the insects which they catch on the wing, and even sorting out their own echoes from those of other bats.

The mathematical technique of decomposing 'wiggling waveforms into sine waves which can then be summed again to make the original wiggly line is called Fourier analysis, after the nineteenth-century French mathematician Joseph Fourier. It works not just for sound waves (indeed, Fourier himself developed the technique for a quite different purpose) but for any process that varies periodically, and it doesn't have to be highspeed waves like sound, or ultra-high-speed waves like light. We can think of Fourier analysis as a mathematical technique which is convenient for unweaving 'rainbows' where the vibration that makes up the spectrum is slow compared with that of light.


Folksonomies: hearing fourier analysis sound

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Wave (0.985015): dbpedia | freebase
Sine wave (0.904473): dbpedia | freebase
Sound (0.857915): dbpedia | freebase | opencyc
Joseph Fourier (0.813371): dbpedia | freebase | yago
Vibration (0.807512): dbpedia | freebase
Fourier analysis (0.643496): dbpedia | freebase | yago
Mathematical analysis (0.615389): dbpedia | freebase
Phase (0.582387): dbpedia | freebase

 Unweaving the Rainbow: Science, Delusion and the Appetite for Wonder
Books, Brochures, and Chapters>Book:  Dawkins, Richard (2000-04-05), Unweaving the Rainbow: Science, Delusion and the Appetite for Wonder, Mariner Books, Retrieved on 2011-09-21
Folksonomies: evolution science