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How does the ear pick out so many different sources from an orchestra

Sound is a serial phenomenon. How does the ear pick out so many different sources from a stream, i.e. an orchestra, is there a maximum it can differentiate between, how does it handle this and can/is this used in data transmission now that switching can be achieved at incredible
Andy Putman from West Yorkshire (Age 55+)

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One Response

  1. Hi Andy,

    There are three processes at work here. The first is localisation – it will assist in the differentiation when one is actually present at a concert, and also to a reasonable extent if listening to a stereo recording. When a sound wave approaches the head from any direction other than directly in front there is a time-of-arrival difference between the ears. There is also a tendency for the head to screen the more distant ear, leading to a lesser intensity being received there. The brain makes use of these inter-aural differences to compute sound direction; if it can distinguish different directions it can identify different sources.

    The second distinguishing feature is the timbre of the sound. If a variety of different instruments all played concert A you could distinguish them. If you used a microphone attached to an oscilloscope you would see that, in every case, the sound wave was going up and down 440 times per second. However, the shape of that wave would differ from one instrument to the next. Again, the ear can detect and signal these differences to the brain, which in turn makes use of the information.

    Lastly, for a great deal (all though by no means all) of music there is a structure with which we are familiar. In terms of voices, we know the kind of thing the tenor line (for example) is going to do. This is very much the same as with speech. If someone is talking about a familiar topic you can follow what they are saying, even in quite a noisy environment. When it’s a specialist topic, with some rather uncommon words and sentence structures, then you need a quiet background. Someone familiar with music can pick out a ‘line’ with comparative ease.

    In a sense some of these factors are involved in high-speed data transmission, particularly in fibre optics, where large numbers of ‘channels’ can be superimposed upon the light beam, by employing different frequencies (as in pitch). In radio, particularly when resistance to eavesdropping is required, frequency-hopping can be used. The designated receiver knows at what frequency the next piece of information will be sent – analogous to you knowing how a cadence is likely to continue.

    Happy listening,

    Peter

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