Sound is stored on a computer as a series of samples. Each one is between -32768 and 32767, and there are lots of them – for high-quality sound, 44,100 samples/second.
In this example, we're copying every other sample and playing the new list. Copying every other sample means that we have nearly the same sound, but we're playing it in 1/2 as much time. Thus, we're squeezing the sound and doubling the frequency.
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