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

Use time stretching to change tempo

Changing the speed of a song or other type of audio file can be useful in many different 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 are learning a new language using a set of audiobooks, then 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 simply by altering the playback, however, is that it typically results in changing the pitch, too. If a song's speed is increased, for example, the person singing could end up sounding like a chipmunk.

The Solution: Time Stretching

Audacity Change Tempo Option

If you have used the free audio editor Audacity, then you might have already experimented with the speed controls for playback. All that does is to change speed and pitch at the same time, though. To preserve the pitch of a song while altering its speed (duration), you need to use something called 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.

Importing and Time Stretching an Audio File

  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 on 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, WMA, etc.

  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 in 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. Click Preview to test.

  7. When you are happy with the change in tempo, click 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've made, you can export the audio as a new file. To do this:

  1. Click File > Export.

  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 Options. This will bring up a settings screen where you can modify quality settings, bitrate, etc.

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