can't understand what side-chain compression does.

I was watching this video https://youtu.be/ozseVOOEAHY?t=90 and the audio engineer is using the side-chain on Cubase’s compressor to compress the reverb on the vocals ‘only when the singer is singing’.
I’m confused, I thought that’s what would happen anyway if you have a vocal track that you have a applied an FX channel with a reverb and also have the compression inserted there in the FX channel after the reverb. Doesn’t the compression, and the reverb for that matter, only work when ‘the singer is singing’, when there is something to compress in the signal on the vocal track being routed to the compression?

In case of reverb, the reverb signal is usually still present when the original signal no longer is.

The sidechained compressor in this technique is acting on the reverb when vocal is present so it doesn’t muddy the vocal…it’s basically ducking.
The reverb is compressed (so pushed down in level) when there is singing so the tail of the reverb will appear to swell up in to the spaces between words.

Thank you! :slight_smile: