Driving Opacity with Sound Keys
Recreating the Alias Intro Part 4

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If you are like me, you hate creating bazillion keyframes in your After Effects projects. In the last of our four part series on recreating the Alias intro, we’ll use Trapcode’s Sound Keys plug-in to drive the opacity of our blinking cursor.

In Part 1 of the series, we created a large number of Opacity keyframes to get our cursor to blink on and off repeatedly. Doing this repeatedly gets rather boring after a couple of minutes and trying to get the blinks to correspond to instruments from the audio track can be very difficult. It can be done, but you have to drop a ton of Markers and make sure you’ve got rhythm, which as anyone who has seen me dance knows I ain’t got. It is much easier to have an assistant – in this case Trapcode’s Sound Keys – to help us out.[an error occurred while processing this directive]Most of us are probably familiar with Trapcode’s other offerings (Shine and 3D stroke), but may not be familiar with Sound Keys. In a nutshell, it is a plug-in that allows you to analyze an audio layer in your Timeline, generate keyframes from that audio and then apply the data to other layers in your Composition via expressions.

“Now wait a minute,” you say. “After Effects already has a brand new Convert Audio to Keyframes feature, and as you have pointed out in your most excellent tutorial on the subject, does exactly the same thing as you just described. What’s the dealio with that?”

Well dear reader, while Convert Audio to Keyframes does generate keyframes based on an audio layer, and while those keyframes can be tied to other layers, CAK should be thought of as an “analyze entire audio track” feature. What sets Sound Keys apart is the fact that you can analyze a specific frequency, or range of frequencies, to pull data from. What’s more, Sound Keys has three range selectors that allow you (or rather After Effects) to analyze various portions of the audio track in a single click.

For example, let’s say you have the Go-Gos’ “We Got the Beat” as your audio layer. You can use Sound Keys to analyze the drumbeat, cymbal crash, and even bass instrument, and then take the results and apply them to three different layers in your composition. Trapcode provides a sample of this in action.

So let’s put Sound Keys into action for our Alias intro.

Step 1: In After Effects import your audio file and add it to your Timeline.

Step 2: Create a New Solid that is the size of the composition. This makes it easier to see the Sound Keys audio spectrum.

Step 3: To the Solid Layer, apply the Sound Keys effect. The controls for Sound Keys are easy to comprehend. Begin by selecting your audio layer and which channel (left or right) you want to use. Then use your Range Selector to select the frequency or frequencies you wish to sample.

Even though I am only using a single instrument in this example, I have selected just one small range for Sound Keys to pull data from.

Because we want to Opacity to be either completely opaque or completely transparent, we really don’t want to see a gradual fade as the intensity of the frequency changes. Instead we can set the Type to On/Off Trigger.

When the intensity of the frequency moves past the selector area (a single line) it sets the Range Value to 100%. When it is below the line it is at 0%.

When you are finished setting the range and type of analysis you want Sound Keys to do, click on the Apply button and let the plug-in do it’s thing.

Step 4: In the Timeline, select the Sound Keys layer and press the U key to bring up all of the keyframes for that layer. Then, select the Cursor layer in the Timeline and press T on the keyboard to bring up the Opacity Property for the layer.

Step 5: To link the two layers together, we’ll have to use an expression. And because we are being lazy we’ll let After Effects do the work for us. Option+click (Alt+Click on the PC) on the Stopwatch Icon to activate expressions for the Opacity Property.

Step 6: Use the Pick Whip, to connect the Opacity expression to the keyframes created in Output 1.

Step 7: Turn off the visibility for the Sound Keys layer so the sound spectrum doesn’t render. Make a RAM Preview and view the results.

After putting the information from these last four exercises together, along with your own creativity, you should be able to recreate the remainder of the Alias intro on your own. Have Fun!

When not working deep in the labs of the DMN Central Division testing the latest and greatest software/hardware products Stephen Schleicher can be found at the local university teaching a few courses on video and web production. He can be reached at [email protected]. You can also visit him on the web at www.mindspring.com/~schleicher

Source: Digital Media Online, Inc

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