when you have your audio, right click the audio layer and click keyframe assistant and then convert audio keyframes
Then when it creates a new layer called audio amplitude, click on it and go to effects and then both channels this is where you will find the slider effect. By clicking on the graph button you can see the slider points of the audio and you can edit them. Attach the shape scale to the slider of the audio you want to parent it by using the pick whip tool of the shape scale to the audio slider.You can edit the slider points by selecting them all and making them bigger and smaller. By doing this it also edits the size of your attached shape to make the size become bigger when the slider points are higher.
Lily
Lily 