You've used the keyframe assistant to convert your audio track to keyframes. Now what? The easiest answer (don't be scared) is to write an expression. To get a full grasp of expressions, be sure to look at Chapter 13. Here's a simple expression to tie the scale of a layer to the beat of audio.
Generate audio keyframes, as described in the previous section ”It's Got a Great Beat.
Highlight the layer to be animated. Press S for Scale. If it is a Text Layer in AE6, choose Animate>Animate Text>Scale.
Enable an expression by selecting Animate>Add Expression or pressing Option+Shift+= (Alt+Shift+=).
From the Expressions submenu, choose Property > value. Property>Value.
As the text appears to grow, multiply the value by a decimal, such as .25.
Expose the keyframes on the Audio Amplitude Layer. Select the Layer, and press U (for user keyframes).
Use the Pickwhip (looks like the @ symbol) to drag it to the desired keyframes.
Check your expression, which should look like this: value*.25*thisComp.layer("Audio Amplitude").effect("Left Channel")("Slider").
Preview the work area to test your animation.