The Convert Audio To Keyframes keyframe assistant analyzes audio amplitude within the work area and creates keyframes for audio amplitude.

This keyframe assistant creates a new 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, you must 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 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: www.adobe.com/go/learn_ae_aharonwaveform.

The Trapcode Sound Keys effect also converts audio values to keyframes, but provides more control than the built-in Convert Audio To Keyframes keyframe assistant: www.adobe.com/go/learn_ae_trapcodesoundkeys.