# How do you adjust tempo without changing pitch?

**URL:** <https://boards.straightdope.com/t/how-do-you-adjust-tempo-without-changing-pitch/645290>\
**Category:** Factual Questions\
**Created:** [December 27, 2012, 4:12pm UTC](https://boards.straightdope.com/t/how-do-you-adjust-tempo-without-changing-pitch/645290 "2012-12-27T16:12:23Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\
**Post date:** [December 27, 2012, 4:12pm UTC](https://boards.straightdope.com/t/how-do-you-adjust-tempo-without-changing-pitch/645290/1 "2012-12-27T16:12:23Z")

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How do audio editing programs like audacity change the tempo of a track without altering the pitch?

The only thing I can think of is some sort of sampling algorithm that expands or contracts each snapshot to change the tempo.

I’ve tried changing the tempo on a few different tracks, and hear no change in the pitch of the notes, just their duration.

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**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\
**Post date:** [December 27, 2012, 4:17pm UTC](https://boards.straightdope.com/t/how-do-you-adjust-tempo-without-changing-pitch/645290/2 "2012-12-27T16:17:08Z")

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Just sing or play faster or slower. (I just read headers.)

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**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\
**Post date:** [December 27, 2012, 4:22pm UTC](https://boards.straightdope.com/t/how-do-you-adjust-tempo-without-changing-pitch/645290/3 "2012-12-27T16:22:43Z")

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I believe the programs effectively “slice” the sound and then fill the gaps by interpolating the pitch between “slices”. I remember dance tracks that used early versions of this software had a distinctive kind of “pulsing” where it wasn’t filled smoothly. Think “Higher State of Consciousness” by Josh Wink, for instance.

Edit: see [Audio time stretching and pitch scaling - Wikipedia](http://en.wikipedia.org/wiki/Audio_time-scale/pitch_modification)

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**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\
**Post date:** [December 27, 2012, 5:00pm UTC](https://boards.straightdope.com/t/how-do-you-adjust-tempo-without-changing-pitch/645290/4 "2012-12-27T17:00:43Z")

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Yup. Chop it up into samples that can be thought of as little packets of a single frequency - then replay all those individual samples for longer or shorter durations as required.

Or do the opposite - shift their frequency and play them for the same duration - and you can change pitch without affecting tempo.

This is how autotune works - the smaller the change you make, the easier it is to accept as natural.