Use Audacity to Change a Song's Speed Without Affecting its Pitch

Use time stretching in Audacity to change tempo while preserving pitch

Audacity Change Tempo Option
Image © Mark Harris

Changing the speed of a song or other type of audio file can be useful in many different scenarios. You may, for example, want to learn the lyrics to a song, but can't follow the words because it plays too quickly. Similarly, if you are learning a new language using a set of audiobooks, then you may find that the words are spoken too quickly -- slowing things down a bit could improve your learning speed.

However, the problem with changing the speed of a recording simply by altering the playback is that it typically results in the pitch being changed too. If a song's speed is increased, for example, the person singing could end up sounding like a chipmunk!

So, What is the Solution?

If you have used the free audio editor, Audacity, then you might have already experimented with the speed controls for playback. But, all that does is to change speed and pitch at the same time. In order to preserve the pitch of a song while altering its speed (duration), we need to use something called time stretching.  The good news is that Audacity has this feature -- that's when you know where to look.

To find out how to use Audacity's built-in time stretching option to alter the speed of your audio files without affecting their pitch, follow the tutorial below. At the end, we'll also demonstrate how to save the changes you have made as a new audio file.

Get The Latest Version of Audacity

Before following this tutorial, ensure you have the latest version of Audacity. This can be downloaded from the Audacity website.

Importing And Time Stretching an Audio File

  1. With Audacity running, click the [File] menu and select the [Open] option.
  2. Choose the audio file you want to work on by highlighting it with your mouse (left-click) and then clicking [Open]. If you get a message saying that the file couldn't be opened, then you'll need to install the FFmpeg plugin. This adds support for a lot more formats than Audacity comes with such as AAC, WMA, etc.
  1. To access the time stretching option, click the [Effect] menu tab and then choose the [Change Tempo...] option.
  2. To speed up the audio file, move the slider to the right and click the [Preview] button to hear a short clip. You can also type in a value in the Percent Change box if you prefer.
  3. To slow down the audio, move the slider to the left making sure the percent value is negative. As in the previous step, you can also input an exact value by typing a negative number in the Percent Change box. Click the [Preview] button to test.
  4. When you are happy with the change in tempo, click the [OK] button to process the whole audio file -- don't worry, your original file won't be changed at this stage.
  5. Play the audio to check that the speed is OK. If not, repeat steps 3 to 6.

Permanently Saving The Changes to a New File

If you want to save the changes you've made in the previous section, you can export the audio as a new file. To do this, follow the steps below:

  1. Click the [File] menu and choose the [Export] option.
  2. To save the audio in a particular format, click the drop-down menu next to Save as type and choose one from the list. You can also configure the format's settings by clicking on the [Options] button. This will bring up a settings screen where you can modify quality settings, bitrate, etc.
  1. Type in a name for your file in the File Name text box and click [Save].

If you get a message displayed saying that you can't save in the MP3 format, then you'll need to download and install the LAME encoder plugin. For more information on installing this, read our Audacity tutorial on converting WAV to MP3 (scroll down to the LAME installation section).

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