Hello, and welcome back to the Soundcraft Ui series video manual series. Today, we’ll be covering the sidechain compression feature of the Ui24R, introduced in the 2.0 Firmware update. Before getting started, make sure that your mixer is updated to the most recent firmware version. Instructions for updating can be found in our firmware update video, and links to instructions will be in the description below. The examples I’m going to show today are best enjoyed through headphones to really experience the compression. Let’s get started. 
Sidechain compression is when we have a compressor on one audio channel that listens to another different audio source to dynamically alter our compressed signal. One example of this is when we have clashing sources like a kick drum and bass sound. Here, I’ve got a kick and a really big bass sound. We can see from the RTA that there’s a lot of overlap in frequencies here in the lower side of the spectrum, and we might describe the sound of them playing together as “muddy” because there’s a lot going on here. A common use for sidechain compression would be to apply the sidechain compression to our bass signal, so that it compressors, or ducks the bass whenever our kick drum comes in. 
First, we need to head over to our subgroup setup. Sidechain inputs are only available on our subgroup compressors. Select the meter view in the top left corner of the interface, then select the SUBS tab to access the sub group setup. Let’s place our kick drum in sub group 1, then our synth bass in sub group 2. Next, head back to the main mix, slide over to see our sub groups, and double click or tap sub group 2 to access its DSP. In the compressor tab, you’ll notice this Ducker option on the top of our parameters. It’s important to remember that a sub group’s sidechain input can only come from lower sub groups. If we click here, we see that sub group 2 can only listen to subgroup 1, our kick drum in this instance. If we look at sub group 6 though, we can see that it has the option to listen to any other sub group, while sub group 1 has no sidechain option.
I’ve set here a low threshold with a high ratio so that we can really hear the change happening, but you will probably want more subtle compression on a traditional kick drum with a bass guitar for example. I’m going to play the two bar synth loop with the compressor bypassed, then enable it for the following bars to hear the difference. You should be able to feel the bass getting out of the kick drum’s way as the bass sound reduces volume and returns, resulting in that pumping feeling that sidechain compression is typically known for. We can also see here that the compression meter responds to the kick drum, and see the difference here when I change the sidechain source to none, so it is compressing off its own signal. One important thing to remember is that the sidechain input pulls its source pre-fade, so the sidechain compression will still occur, even if I mute the sub group with our kick.