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Sound waves are recorded as waves electronically. What I am asking is how these waves are 'sped up'. For example on a sound software, when you get a sound wave and then speed it up (using some editing tools), what does the computer do to speed it up?


Images to show what I mean:

How does a sound wave go from this

enter image description here

To this

enter image description here

When I speed it up to 200% of its original speed.

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  • $\begingroup$ This might be better-suited to dsp.se. $\endgroup$
    – J.G.
    Jul 28 at 19:43
  • $\begingroup$ The relevant term is sampling frequency, which tells you how many samples of your recording were taken per second. If you later play it via your speakers at higher sampling frequency, thus playing more samples per second, it will take less time to play the whole recording wright? $\endgroup$
    – Yair M
    Jul 28 at 20:23
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When stored digitally, audio is a bunch of data points where each data point is an amplitude sample and an associated time that it occurs at.

To speed something up (or slow it down) you just change the time that the sample occurs at (i.e. decrease or increase the time between each sample).

It's the digital equivalent of literally turning the casette tape reel or vinyl record faster (you know what those are right?)

It's almost identical to just hitting the notes on a piano faster when reading sheet music.

But unlike a piano where you are just speeding up when the notes play rather than the sound of the note itself, everything will also sound higher pitched since all signals are composed of a bunch of sinusoids superimposed (stacked up) on each other via Fourier analysis (which you might not have heard of yet seeing as your profile says you are quite young) so when you play everything in the signal faster you are basically running through the constituent sinusoids faster which makes them higher frequency.

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