The Standing Invitation

Quieten Down

with 5 comments

I dislike noise. When I go to a pub I go there to listen to people, and there is nothing I hate more in a night out than not being able to hear what they are saying.

When you listen to someone speak, you are trying to detect with your ears the audible signals they produce with their mouths; noise is everything you hear that is not a signal. How well you can hear a person depends on how clearly their words stand out against the background: the signal-to-noise ratio.

Signal-to-noise ratios appear everywhere in science where a precise measurement must be taken. In order to understand measurement ­– in order to comment on what it is we can ever hope to know about the world – we have to have a working knowledge of the properties of noise.

Now noise from a Shannon-information perspective is anything that disrupts a flow of information, but generally speaking it is useful to separate noise into two different types: intrinsic noise (or thermal noise), and extrinsic noise (or interference).

Let’s say you want to use a microphone to measure some very faint sound – the sound of an ant chewing a leaf, say. Plug in your headphones and the first thing you’ll hear will be a your neighbour’s washing machine, or traffic on the street outside. This is extrinsic noise and can be reduced by shielding. People build anechoic chambers to reduce extrinsic noise: carefully insulated and coated with foam pads to deaden echoes, they offer some of the quietest places on Earth. According to John Cage, his piece 4’33” was inspired by his experience in an anechoic chamber. Expecting to hear nothing but peaceful silence, he was surprised to hear

two sounds, one high and one low. Afterward I asked the engineer in charge why, if the room was so silent, I had heard two sounds. He said, ‘Describe them.’ I did. He said, ‘The high one was your nervous system in operation. The low one was your blood in circulation.’

What Cage experienced was intrinsic noise, noise that no soundproofing can remove because it originates inside the thing doing the measurement. In his case, the noise came from inside his body, but even an electronic microphone will hiss and crackle from the random motion of electrons in its wiring.

No analytical tool is safe from intrinsic noise, not even a simple ruler, whose length fluctuates randomly on a scale too small for us to notice, but is sufficient to preclude its use for measuring things on the molecular scale. This is all because everything, ultimately, is made of particles that are always in motion ­– tiny, incessant, random movement caused by the ambient temperature.

So that background hiss interfering with your measurement will never go away. It is also totally random ­– and yet, as a consequence of this randomness, it is in some ways completely predictable. Some maths shows, for example, you can increase the accuracy of your measurement simply by taking lots of measurements and averaging them out: the more measurements you take, the more your signal stands out against the background noise. More exactly, if you take four times as many measurements, your signal-to-noise ratio doubles.

But measurements can be costly; noise can never be removed completely; and there is a law of diminishing returns. If a measurement with precision x costs you £10, twice as much precision would cost £40; twice as much again would cost £160. Sometimes the size of the error bars depends on how much you can afford.

REFERENCES

http://cm.bell-labs.com/cm/ms/what/shannonday/shannon1948.pdf

http://www.physics.utoronto.ca/~phy225h/experiments/thermal-noise/Thermal-Noise.pdf

http://www.lichtensteiger.de/anechoic.html

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Written by The S I

October 9, 2011 at 11:59 pm

5 Responses

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  1. Sorry to comment solely on your title, but it’s so intriguing that I can’t help myself. I (think) I normally say “quiet down”, but I know I have definitely heard the phrase “quieten down” as well. To me, the -en is odd. An extra syllable that trips me up, especially because I would pronounce it [kwaiəʔən]. The -en ending is a derivational suffix that roughly means “become more [adj]”. So verbs like “quicken, lengthen, darken, redden, widen, etc.” all have to do with something becoming *more* whatever the quality of the verb is. Apart from the pronunciation, three things make the word “quieten” odd for me: 1) the adverb ‘down’ already conveys the semantics of ‘become’ (for me). I picture the sound going down just by virtue of the the adverb down, so the -en ending is redundant. Semantically “quieten down” conveys “become more quiet cause the sound to go down”. Secondly, the phrase is an imperative – a mood that usually consists of just the root of the verb. If I say “quiet!” I’ve successfully given a command, just as surely as I’ve given a command if I say “stop!” What’s more, this imperative (quiet!) already has the sense of ‘become’ built in to it. Of course, you can also say “Quick*en* your pace!”, “Wid*en* the road!” ect., and you certainly can’t say “*Quick your pace!” or “*Wide the road!” (though you could say “Quick!” and mean ‘be quick!’). So I started thinking of other examples of imperatives and verbs ending in -en. Then I realized that they all had monosyllabic roots: ‘quick’, ‘length’, ‘dark’, ‘red’, ‘wide’. When we add another syllable, we’re left with a nice comfortable iamb. Quieten, on the other hand, is an awkward dactyl. Not that I’ve actually taken the time to look up whether we have a preference for iambs or dactyls in idioms as it’s 1am, but I think there might be something to it. So I think the -en ending was added to ‘quiet’ in the phrase ‘quieten down’ to add emphasis to the becoming aspect. Perhaps “Quiet!” has 1 unit of emphasis, “Quiet down” has 2, and “Quieten down” has 3. In that case, a need for emphasis could override a need for an iamb, thus resulting in the phrase “Quieten down”. Maybe. Possibly. Who knows? It’s 1 in the morning. Also, allow me to throw in the disclaimer that neither is ‘better’ or ‘more correct’ than the other, they just place emphasis on different rules, which are mutually exclusive. It’s like a chocolate or vanilla sort of thing, i guess.

    Devon

    October 10, 2011 at 1:17 am

  2. That is possibly the most research on a two-word title I think I’ve seen. I did actually have to check that ‘quieten’ was in regular usage; I was sure I’d heard it before, but it sounds strange even to me. I guess it’s actually pretty rare these days. Is quieten uniquely British English? Do Americans use it at all?

    The S I

    October 10, 2011 at 7:28 am

    • I’m certain I’ve heard it in places not the UK, but it has a sort of quaint charm to my ear. I actually think it sounds a bit Pennsylvania Dutch, on a purely aesthetic basis. Most of my google results were for British usage. The people on this forum seem to agree: http://wordwizard.com/phpbb3/viewtopic.php?f=7&t=21826 .

      Devon

      October 10, 2011 at 1:57 pm

  3. I’m guessing you’ve heard about the Holmdel Horn Antenna?
    It was built in the 60s for satellite communications experiments, and they kept getting 3°K of background noise in every reading. After trying all sorts of things to clear it, and consulting various other specialists, the ‘noise’ eventually turned out to be the first ever observation of cosmic background radiation. Thus the HHA, and the two radio astronomers working on it, became better known for their contribution to the Big Bang theory than whatever it was the thing was supposed to do.

    Daniel Tysen

    November 4, 2011 at 4:01 pm

    • I don’t know how many examples there are of something this wonderful happening in science, but there can’t be many.

      The S I

      November 4, 2011 at 4:37 pm


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