How to Modify a Song's Playback Speed Using Audacity

The free audio editor Audacity has a playback speed control that also changes the pitch. To preserve the pitch of a song while altering its speed, use Audacity's time-stretching feature. Follow these instructions to learn how to use Audacity's built-in time-stretching tool, and how to save the changed files.

Import and Time Stretch 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.

   Before you download and use Audacity, review its privacy policy to ensure you're in compliance.

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 cannot be opened, install the FFmpeg plugin. This adds support for more formats than Audacity comes with, such as AAC and WMA.

4. Select a stretch of audio and choose Effect > Change Tempo to access the time-stretching option.

   Press Command+A to select the entire file.

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.

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.

Save Changes to a New File

If you want to save the changes you made, export the audio as a new file. Here's how:

1. Select File > Export and choose a format type.

   Whichever file format you select, you have the option of changing it in the window that appears.

2. 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).

Why Change the Playback Speed?

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 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.