How to Modify a Song's Playback Speed Using Audacity

Use time stretching to change tempo

What to Know

  • Open an audio file by going to File > Open. Select Effect > Change Tempo.
  • Then, move the tempo slider. Select Preview to hear changes and select OK.
  • To export the audio as a new file, go to File > Export. Choose a format and select Save.

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

The problem with changing the speed of a recording by altering the playback, however, is that it typically results in changing the pitch, too. If a song's speed increases, the person singing could end up sounding like a chipmunk.

The Solution: Time Stretching

If you use the free audio editor Audacity, you might have experimented with the speed controls for playback. All that does, however, is change speed and pitch at the same time. To preserve the pitch of a song while altering its speed (duration), use time stretching. The good news is that Audacity has this feature.

Follow the tutorial below to learn how to use Audacity's built-in time-stretching option to alter the speed of your audio files without affecting their pitch, and how to save the changed files.

Before you download and use Audacity, be sure to review its privacy policy to ensure you're comfortable with its terms.

Importing and Time Stretching an Audio File

Follow these steps to modify a song's playback speed in Audacity.

  1. Ensure you have the latest version of Audacity. You can download it from the Audacity website.

  2. With Audacity running, select File > Open.

  3. Choose the audio file you want to work on by clicking it and selecting Open.

    If you get a message saying that the file can't be opened, install the FFmpeg plugin. This adds support for many more formats than Audacity comes with, such as AAC and WMA.

  4. To access the time-stretching option, choose Effect > Change Tempo.

  5. To speed up the audio file, move the slider to the right and click Preview to hear a short clip. You can also type a value in the Percent Change box if you prefer.

    Audacity Change Tempo Option
  6. 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 enter an exact value by typing a negative number in the Percent Change box. Select Preview to test.

  7. When you are happy with the change in tempo, choose OK to process the whole audio file. Your original file remains unchanged at this stage.

  8. 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 made, you can export the audio as a new file. To do this:

  1. Select File > Export.

  2. To save the audio in a particular format, click the Save as type drop-down menu and choose one from the list. You can also configure the format's settings by choosing Options. This brings up a settings screen where you can modify quality settings, bitrate, and more options.

  3. Type a name for your file in the File name text box and select Save.

If you see a message saying that you can't save in the MP3 format or you receive a lame_enc.dll error, download and install the LAME encoder plugin. For more information on installing this, read this Audacity tutorial on converting WAV to MP3 (scroll down to the LAME installation section).

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