This keyframe assistant creates an Audio Amplitude layer representing all audio sources in the composition, with three Expression Controls effects with Slider properties that contain the keyframes: Left Channel, Right Channel, and Both Channels.

To make use of the keyframes created by this keyframe assistant, link the changes in audio amplitude to other layer properties. For example, use an expression to link the audio keyframes to the Scale property of a layer to make the layer grow and shrink as the amplitude increases and decreases.

Aharon Rabinowitz provides a video tutorial on the Creative COW website that shows how to link the audio amplitude keyframes to other properties—in this case the properties of the Wave Warp effect, to synchronize animation with sound.

John Dickinson provides a video tutorial on his Motionworks website that shows how to use the Convert Audio To Keyframes keyframe assistant to animate the opacity of a layer and one of the properties of the Grid effect to the beat of the music in a soundtrack.

Satya Meka provides a tutorial and animation preset on his website with which you can generate animations based on separate audio frequency ranges.