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General Asylum General audio topics that don't fit into specific categories. |
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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Re: Simple Technical Question posted by TomLarson on March 2, 2007 at 11:17:06:
Frequency defines a repetition in time. 20 Hz is 20 times a second, 20 kHz is 20,000 times a second. Frequency is established over time.At a fixed point in time, frequency disappears. If you could take a measurement of sound at a single instant, with no information from any instant before or after the instant at which you took that measurement, you would get amplitude information but nothing that would allow you to determine the frequency of the sound. That's because there is no variation in that single instant. The variation in amplitude that determines frequency occurs from instant to instant.
At any given instant, the speaker driver is only producing amplitude information, but that amplitude is in constant change. It's the changes from moment to moment that produce the frequency information. So the question becomes how do we get to hear different notes simultaneously when all that the speaker is doing is delivering amplitude changes. Think of an oscilloscope trace for a pure sine wave, a single tone, then of the trace for the same sine tone with some harmonic distortion added in. It's still recognisably a sine wave but it's no longer smooth, and it's that loss of 'smoothness' in the sine wave pattern that causes us to hear the overtone structure of the tone. Now, go back to that 'scope pattern with the added overtones in it and freeze it at a particular instant. What have you captured? Amplitude information only - you've got a single value, just as you have with the pattern for the pure tone. Comparing the results of measurement at a single instant in time for the pure tone and the tone with overtones, the only difference in your measurements is going to be a difference in amplitude. You won't be able to tell from a measurement at a single instant whether the sound is a pure tone or a tone with an overtone structure. It's amplitude change in time that delivers the frequency info.
I was a bit surprised by this answer when I first read the responses in this thread but then I thought about it and realised that the answer is correct. It seems incredibly counter-intuitive but life is full of surprises.
David Aiken
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- Re: Simple Technical Question - David Aiken 13:12:11 03/02/07 (0)
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