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Linking Audio in After Effects

Using waveforms to modify effects By Paul van der Spek
Using the audio levels from a specific layer, you can link and control various parameters from effects within After Effects.  Using expressions to help link the effect parameter to the audio keyframes will make the project run quickly and easily.After reading this tutorial you will be able to link the audio of your movie to an effect so the effect will react depending on the sound variables of the movie you have chosen to use.

There are only a few simple steps you need to learn.  After you know these, you can apply them to other effects to create a wide range of animations.

1. In After Effects create a new composition, the same length as your movie.    To do this first import your video footage. (right click in the project window (Import File)). Now click on your video footage and drag it to the icon below.

You'll have to find your own movie that has an audio file attached the one that is used for this tutorial is attached as a reference.

2. Right click on your video footage again but this time do it in your timeline window and go to Keyframe Assistant Convert Audio to Keyframes. A Null Object with the name ?Audio Amplitude will appear. Select the Null Object layer and press ?U on your keyboard to show the changed parameters of that layer.

click for larger image

3. Now you can apply any effect to your video footage layer. For this tutorial I applied the effect called ?Trapcode Shine to it. You can download the trial for free at  http://www.trapcode.com.

I used these settings:

4. This tutorial is about linking a certain effect to the audio of your video footage. Actually its not about linking a certain effect, but its about linking a certain parameter of that effect to your video footage. We can now decide which parameter we want to link to our audio. We could link the RayLength to the audio, or the Boost light etc. I chose to let the Ray Lenth react on the audio. To do this we need to set an expression for the Ray Length.

 An expression is basically a way to let After Effects relate layers to eachother. If you want to know more about expressions check out some other tutorial about them because I wont go into it any further.

 To set an expression for the Ray Length or whatever parameter you want to use, just ALT + Click on the stopwatch which is located at the left of the parameters name.

 5. Now the way to link this parameter to the audio is click on the ?Pickwhip icon (the icon which looks like a Twirl) and hold it and drag it to ?Both Channels slider parameter. The screenshot below will explain it better.

You just linked the Ray Length parameter to the audio of your video footage. So if the volume of your video footage increases, so will the Ray Length. Of course you could also apply this same technique to the Boost Light parameter and so on.

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Paul van der Spek is an animator from the Netherlands.  He specializes in logo illustration, logo animation as well as promo graphics.  His current software is Adobe After Effects, Autodesk 3DS MAX, and MAXON's CINEMA 4D.  He is also participating in the current public beta of Photoshop CS3.   Not only an animator, Paul stays current with sports and is also a gymnast an avid tennis player.  You can contact him for work by writing to PAULSPEK [at] gmail.com.
Related Keywords:Tutorial, audio, expressions, adobe after effects, Trapcode Shine

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