The text layer includes several properties that you can animate with audio keyframes. To animate the size and color of the text layer, add an expression to the text layer’s Scale property. Later you’ll add an expression to the Hue property.

Expressions let you animate effects and properties by using mathematical variables, or by linking keyframes between layers with the pick whip.

Select the text layer and press the S key to reveal the layer’s Scale property. Then, select the Scale property and choose Animation > Add Expression. Drag the expression’s pick whip to the Both Channels slider for the Audio Amplitude layer.

Now, preview the composition to see how the audio keyframes adjust the scale of your text layer. Select the Audio button in the Time Controls palette to include music in your preview, and then click the RAM Preview button.

Audio amplitude values tend to be low. As a result, the text is likely to be too small. To increase the size, or scale, add a multiplier to the expression. Because expressions are too long to view in their entirety within the Timeline window, make edits by clicking anywhere in the expression and navigating with the right and left arrows. Type *10 after each of the two ("Slider") values to magnify the amplitude by a factor of ten, thereby increasing the scale by a factor of ten. Click anywhere outside the expression to exit the edit mode. Try different multipliers to get the look you want.

Your final expression should look like this:

[thisComp.layer("Audio Amplitude").effect("Left Channel")("Slider")*10, thisComp.layer("Audio Amplitude").effect("Right Channel")("Slider")*10]