Linear expression

- In this After Effects Hidden Gem,…I want to teach you how to use an expression…that would probably intimidate you at first,…but it's really useful:…it's the linear interpolation expression,…and what it does is convert any one range of numbers…into any other range of numbers.…It's a great way,…when you're trying to coordinate animations,…to make two different ranges,…such as rotation and, say, something like opacity…or tracking or blur amount,…line up to do what you want them to do.…Now, you might have seen this composition before.…We used it in the previous Hidden Gem,…when we were showing how to extract keyframes from audio.…

Here is our audio track,…(rhythmic techno music)…and to convert that into keyframes,…we go to Animation, Keyframe Assistant,…Convert Audio to Keyframes.…This creates a null object…with three expression controls attached:…one that has the left channel's volume,…one that has the right channel's volume,…and one that has both channels together.…I'll twirl these up, twirl up the waveform,…and focus just on the both-channels slider for now.…