Sound Advice

To make attributes of an effect or layer react to audio amplitude...

I start by creating a new composition and new solid. I need to generate audio keyframes so I go to keyframe assistant and then convert the audio to keyframes. Now a new layer of keyframes has been created and this is also represented by a null object in the project which we might as well move to one-side. If we look at the audio amplitude layer we see keyframes for both the left and right audio channels and for both (their mono signal). I then go to my new solid and say I want to effect the scale, I open up its transform options and holding the alt key I click on scale and now the expression controls are open for that parameter. I can now use the pick whip to link the scale to the amplitude of whichever channel I desire. Still it is often the case that the scale of the solid won't correspond nicely to the amplitude of the audio. We might not want the solid to be next to invisible when there are quiet patches. So we go back to the expressions of the solid and in the box for writing the expressions code we remap it. All this entails is clearing what's there and writing "linear" in lower case and then follow that with no space with (value,0,40,20,100) so the whole thing looks like this; linear(value,0,40,20,100). Please note that the numbers I've used in the brackets are only examples. The first two numbers are the original scale that the amplitude was adhering to so in this case the solid was at its largest when the audio was at 40 and was invisible at 0. Now it will always be seen at a corresponding size of 20 units and can go up to 100. These principles can be applied of course to pretty much anything keyable.