October 05, 2017

Side Chain Compression in Reaper, Ducking for Voice Overs - iBT-094

23 minutes

Setting up a side chain in reaper is relatively straight forward. First what is a side chain? There’s many situations in which a side chain could be useful, and I will show one example today. In essence, a side chain is where you use the output of one track to control the effects on another track.

The example I’ll go through is where you want to have your background music on one track automatically lowered in volume, or ducked, when there is speech on another track. So for example your podcast intro music is ducked when you start speaking.

As usual I’ll demo this on the Mac, however you can follow the same process on windows.

Before we start there’s a couple of other concepts to cover, and the first part of the tutorial is some revision of concepts already covered in this series. This includes a little on recording, editing with items, and the impact of your ripple setting.

The tutorial also briefly introduces a couple of the available ways to normalise audio within reaper.

So let’s look at the basic way audio flows through reaper in a simple default setup. Whether the source is your Microphone or a file you’ve inserted on a track, the source will have an inherent volume as it comes in and goes on to the track. You can adjust the volume of the file or add input effects as it comes in and goes on the track. Once it hits the track you can also add effects and adjust the volume/pan of the track. The audio is then routed on to the Master track along with other tracks in the project. Once again you can adjust volume/pan, and add effects at this stage. It is the output of the master track that you then hear through your hardware outputs and what is printed to any file that your render.

You can set up sends or receives which are basically just sending the audio from one track to another track before it reaches the master track. So for example, audio from a number of vocal tracks could be sent to a track that has a reverb instantiated on it. In this way, rather than setting up multiple copies of a reverb on multiple tracks, one copy of the reverb can be set up and the audio of a number of tracks can be affected by it. The audio that is on the original track can be optionally sent to the master track or not, depending on the specific requirements.

In the side chain we will be setting up in this tutorial, we will be sending the audio from our vocal track to the music track. We will still want the vocal track to go straight to the master track so we can hear it. The copy that is sent to the music track will not be heard in the master however it will be used to compress the volume of the music, or in other words, to duck the music.

We have a track with music, and a track with a voice over. To set up the side chain, go to the music track and press “I”. This will bring up the routing for the track. First step is to change the music track from a standard 2 channel stereo track to a 4 channel track. Next setup a receive from the vocal track to the music track. Next, set the destination of the send from the vocal track to the third and fourth tracks of the music tracks. You will then have a copy of the audio from the vocal track being sent to the music track, however instead of being mixed with the first and second channels, it will be received on the third and fourth channels, and won’t be actually heard in the output of the track. In this way it can influence effects that are applied to the music track even though it won’t be heard there.

Now, we can add a compressor to our music track. In this tutorial, we are using the included compressor, Reacomp. Set the detector input of Reacomp to aux 3/4. This means that it will compress the audio on the music track, but instead of being triggered by the music, it will be triggered by the audio on the aux channels, that is the vocal we sent to channels three and four.

Finally, we need to set up the compressor suitably to compress the music enough to hear the voice over. Set the ratio to a suitable value, at least 4/1 or higher, in the demo I set it to 6/1. You can use the precomp and attack parameters to affect how quickly the audio is ducked and the release parameter to affect how quickly the audio returns to it’s original volume once the voice over stops. The lower you set the threshold, the quieter the music will be while it is being compressed.

We have now set up a side chain to duck our music while speaking. This may seem fairly complex at first, however understanding the concepts covered will help with lots of task you might want to undertake in Reaper, or any professional DAW

Keyboard Shortcuts

Shift+PageUp/PageDown SWS: Nudge active take volume up/Down

Shift+N Item properties: Normalize multiple items to common gain

Command+Shift+N Item properties: Normalize items

I Track: View I/O for current track

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