To slow down the playback speed of MP3, there are many audio and video editing softwares that can be realized, such as: Sound and Shadow, which are composed of:

1. Open audio and video, right-click audio track-insert audio-to audio track. As shown in the figure below:

2. Click the playback speed, as shown below: Adjust the buttons in the picture to adjust the rhythm.

3. Hold down the shift key and then drag the end of the material. No, you can change the playback speed.

4. After adjustment, click Share to generate a sound file.