# how come when you speed up an audio track, the pitch also (usually) goes up?

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how come when you speed up an audio track, the pitch also (usually) goes up?

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Sound is vibration of air.
Pitch is defined by the number of vibrations per second.

When you speed up an audio recording, you are speeding up the vibrations that happen every second, and therefore the pitch goes up.

EDIT: if something is speeded up from normal speed and the pitch *doesn’t* go up in proportion (e.g. YouTube video speed), that is only possible because of audio processing to retain the original pitch.

pitch is, basically, frequency, as in how many times a sound wave changes in a given time frame (normally a second).

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you speed up a audio track, you make everything happen faster, you increase the frequency, everything is higher pitch.

Imagine sound as a series of pulses. Different pitches have X amount of pulses passing by in certain amount of time. Higher pitches have higher rate of pulses, or a *higher frequency*

When you speed something up, you are making it so all those pulse pass by in a faster amount of time, or a higher frequency… higher frequency leads to higher pitch.

Understanding that but about pulses also reveals this little mind fuck of gem… “Pitch is equal to rhythm”. I always liked how [this video](https://youtu.be/NmeogiNhdHI?t=1782) demonstrated it. (if the time stamp link doesn’t work, skip to 29:42. He shows you that by going from a repeating pulse and speeding it up, eventually you end up with an audible note, and the note’s pitch will keep increasing as the pulses are passing by more frequently. Edit: and he further elaborates on it with chords)

I think [this image will help](https://www.vedantu.com/question-sets/b4470de2-50e2-41be-8357-39782c1791ab7878403365382370013.png)

Imagine those up and downs as the sound wave over time. The long up and downs are a low pitch and the short up and downs are a high pitch.

Now imagine making the top sound wave half as long by stretching it. It would look like the high pitch sound. That’s basically what speeding up an audio track does.

To not change the pitch when speeding a track up software needs to do a lot of work to change the sound waves back to low pitch.

Pitch depends on the frequency of the sound. When you draw out a sound wave, it goes up and down at varying times and varying amplitudes.

Let’s just think of a simple sine wave. It goes up and down repeatedly to the exact same intensity and at the exact same time interval all throughout. If you played a sound like this, it would be a simple tone with a pitch, and not much else going on because it’s a simple one.

If we played this sine wave faster, what we’re effectively doing is taking this sine wave and squishing it from the sides to make it fit in a smaller amount of time. This changes the frequency of it because each peak happens closer together than it did before. All sine waves are the same shape, but squishing and stretching them will change the frequency, and that changes the pitch that you’d hear from it in a speaker.

All sounds will work similarly. Squish it to make it fit in a smaller time frame, and the frequency goes up to keep everything going faster, and faster frequencies in sound mean higher pitches to our ears.

With computers and certain software, you can speed up sound without changing the pitch, because it actually changes the entire shape of the wave to make all the same pitches happen in the same order, but faster. But that’s relatively advanced and uses a lot of calculus