In a new project, import an audio source file, such as a WAV, MP3, AIF or MOV file. Since you’re using the audio’s amplitude to animate the layer, music with a good beat works best, though any audio file will do. Create a new composition and limit the duration to a few seconds to speed up processing and previewing times. Add the audio file to the Timeline window.

Select the audio layer and choose Animation > Keyframe Assistant > Convert Audio to Keyframes. A new null layer called Audio Amplitude appears in the Timeline window with keyframes that contain values for the audio’s amplitude. To view these keyframes, select the Audio Amplitude layer in the Timeline window and press the U key on your keyboard. Leave the layer expanded.

While you could use any type of source footage, text layers illustrate the capabilities of audio amplitude keyframes exceptionally well. Select the text tool in the Tools palette and click in the Composition window to create a new text layer. In the Character palette, choose a font and a font size that’s suitable for the size of your composition. (The composition shown has a 320 x 240 frame size and uses a 48 pixel font.) Leave the remaining controls at their default settings. Click in the Composition window and type a single word. Use the selection tool to reposition the text layer as needed.