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In post-production mixing or audio for video, it's fairly common to use side-chain compressors to duck music and effects under dialogue. This trick is especially handy when deadlines won't allow for time-consuming volume-automation passes. Here's how it works. Listen to this sample dialogue against the unducked music, and notice how the music is way too loud for the dialogue to be clearly audible. (music playing) (Male speaker: This is an example of audio ducking. My speech triggers compression on the music track, but when I stop--) Instead of using automation to turn the music down when the dialogue comes in, I'll try a different approach using the side-chain compressor.
Listen after I engage the side-chain compressor. (music playing) (Male speaker: This is an example of audio ducking. My speech triggers compression on the music track, but when I stop--) So, I start by applying a compressor to the music or effects submix. I'm using the C1 here. Now, because I want the compressor to react to the signal coming from the dialogue, I need to get the dialogue track to talk to the compressor on the music track, using the side-chain input.
In Pro Tools, I do this by creating a send to an internal bus. That send will feed the compressor's side-chain input, which is set to listen to the same bus. In other DAWs, like Logic for example, the key is simply selected from a track list at the top of the plug-in window. So, I'll choose a bus, Bus 1 in this case, and I'm going to bring that level up to around 0. I'm going to make sure that in my key input I've set to that same bus Bus 1 in this case.
Once my side chain is set up and the key is active, I can lower the threshold until I start to get a bit of attenuation on my music mix. Take a listen. (Male speaker: This is an example of audio ducking. My speech triggers compression on the music track, but when I stop--) (music playing) (Male speaker:--the music is allowed to return to its normal volume.) (music playing) When using the compressor to duck music under dialogue, I prefer to use longer release times so the music doesn't creep up between words, especially if I'm doing a significant amount of ducking.
Release times of one to two seconds or more in this case can really give the ducking effect that smooth automation ride sound that doesn't get choppy or cut into the dialogue. Now, even though many compressors can look ahead to anticipate the attack, they don't look ahead far enough to anticipate and duck the music in a subtle way. But this is the beauty of the side chain. We can tell the compressor to work from any signal we want. So, I might send the compressor a signal of a duplicate track of the dialogue that has been pulled earlier in time by one to two seconds and key with that.
This earlier dialogue track can be muted and not heard in the actual mix, while still sending signals through the compressor's side chain. In certain DAWs like Pro Tools, you'll need to use pre-fader sends to achieve this. That way the track's signal still passes audio at its send, but its main output is muted. I've gone ahead and set this up already in a hidden track called Dialogue Early and I've pulled this back one second so that it triggers early. It's been muted with the send set to PRE here. So, let's take a listen.
(music playing) (Male speaker: This is an example of audio ducking. My speech triggers compression on the music track, but when I stop--) (music playing) (Male speaker:--the music is allowed to return to its normal volume.) (music playing) Again, ducking dialogue is a great technique when automation rides would take too much time or you need to affect the work in real time with a live input.
Try this technique the next time you're working on dialogue and music in the same mix.
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