# Change Tempo

### From Audacity Manual

Use the Change Tempo effect to change the tempo of a track without changing its pitch.

  Accessed by: Effect > Change Tempo...

Note: all the input boxes are linked: changing the value in one box will change the values in the others.

## Percent Change

If you know the amount you want to change the tempo of the selection, enter that value in the input box. You can also drag the slider to select a value: the input box will update as you drag the slider.

## Beats per Minute (BPM)

If you know the BPM of the selection and the BPM you want to change it to, enter those values here.

## Length

If you know what you would like the new length of the selection to be, enter that value in the to input box. The from box shows the current length of the selection and cannot be changed. This is useful if you have a piece of narration that is just a little bit too long or too short to fit where you want it.

## Limitations

### BPM Changes

Although you can enter fractional values for the "from" and "to" BPM values, these will be truncated to whole numbers.

To achieve changes between fractional BPM values, use this calculation:

  ( ( (BPM to) - (BPM from) ) / (BPM from) ) * 100 = percent change

For example, if the selection is 138.34 BPM and you need it to be 140 BPM, the calculation is:

  ((140 - 138.34) / 138.34) * 100
  (1.66 / 138.34) * 100 = 1.186%

Enter 1.186 in the Percent Change text box.

### General

Change Tempo is a time-stretching effect, because it defies the normal expectation that reducing the speed of the audio (thus increasing its length) will reduce the pitch and vice-versa. As with any time-stretching effect, some audible distortions will be expected at more extreme settings.

Due to weaknesses in its algorithm, Change Tempo can remove a very short length of content from the start or end of the selection, or not stretch the end of the content to the end of the selection when slowing down. Both of these symptoms may leave a short silence at the end of the resultant selection. To avoid this problem, you can use Effect > Sliding Time Scale / Pitch Shift... instead, setting initial and final tempo change to the same amount.

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