After Effects 6 has a new assistant designed to generate audio keyframes. It sounds great, in theory, until you try to use it. The problem is that the Convert Audio to Keyframes Assistant simply translates the entire audio track to new keyframes. Sure, it splits up the channels, and gives you a combo channel, but it only tracks amplitude.
This generates too many keyframes with very little focus. What would you think if we didn't offer an alternate solution? Here's one that involves a little pre- and postprocessing.
To focus those keyframes, try the High-Low Pass effect (Pro Only). This filter essentially acts as a dam, and blocks frequencies above or below a specified point. For example a Low Pass filter set to 200 kHz will only allow the lowest drums to pass through. If you don't own Pro, use the inferior Bass & Treble Effect.
To further refine the area of focus, use two High-Low Pass Effects. Apply the Low Pass filter first, allowing only sounds below a certain frequency through. This will clip the top parts of the sound. Then follow up with a High Pass filter set to a frequency lower than the first effect. This will drop all sounds below the set frequency, and enable you to specify a range that only allows vocals through.
Highlight the audio track that you have prepped. Select Animation>Keyframe Assistant>Convert Audio to Keyframes. If you have a long sequence (or a slow machine), it's worthwhile to stretch your legs for a few minutes. This assistant can take a while to run.
If you twirl down the parameters on the new track, you'll discover its generated temporal keyframes (and a lot of them at that). This is a great place to use the Smoother (Window>The Smoother). Select the keyframes in question, and apply smoothness with a tolerance setting between 1.5 and 6 (depending on complexity of keyframes). You now have keyframes that are more useful.