Side chains are overrated. Useful? Yes. Cool. Totally. Which is why engineers and teachers love talking about 'em. They require some explaining, which demonstrates, you know what you're talking about and that sells classes. But a side chain isn't an effect. And it's not just the thing that makes your track go. A side chain is just a special way to connect two things together. But to understand it, we need to start at the beginning. There are two main families of effects. You got dumb effects and you got smart effects. Dumb effects are the ones you just turn on and they do something.
Smart effects make a decision, but it's not just compressors, it's auto filters, noise gates, ring modulators, vocoders. Anything that performs logic, like if this happens, then that happens. Those can make their decision based on whatever you choose, and that's what a side chain is. So before the side chain police come for me, I want to tell you that lots of records have been made without ever using one.