Ducking is the term we give to the process that entails one sound or event being used to attenuate (lower in gain/volume) of another sound. The common processor used for ducking is a compressor.
Ducking has been around since the advent of broadcasting. Traditionally ducking is used to manage the volume between the broadcaster and the background music. I am sure you have heard this effect before. Every time the broadcaster speaks the background music lowers in volume.
The most important effect used in music production is reverb. We use reverb more than any other effect and when it comes to vocal treatment we love to splash it all over the place because we believe that the more reverb we apply the more natural space we create for the vocals to sit in. This is where the problems creep in. In today's high track count mixes reverb shows up across multiple sounds and as you already know effects sum just like audio. The more instances of reverb we use the more we eat into the headroom and dull the mix. It is easy to get your mixes to exhibit that horrible 'wash' effect whereby too many instances of reverb start to conflict with each other and smear frequencies. We end up losing clarity for the sake of a big reverb sound. This tends to happen more on vocal channels than anywhere else because we instinctively go for the reverb effect when processing vocals. BUT there is an Old School technique that can help to alleviate this problem and maintain vocal clarity even with such high reverb use.
We use a compressor on the reverb channel (auxiliary) and activate the side-chain. We then send the vocal line to the side-chain. The vocal acts as the trigger. We set the compressor to compress the effect but not to gain compensate too heavily as this negates the whole ducking process. Every time the vocals start to play the reverb is attenuated or ducked and when the pauses in the vocals appear the reverb jumps back up in gain and we can hear it.
You can take this process a step further and use the side-chain filtering on the compressor to turn it into a frequency conscious trigger. In other words we can actually select a frequency range of the vocals to trigger the ducking process.
Let me simplify this tutorial for you and physically show you how we set up and use side-chaining to duck reverb effects on vocals so as to achieve clarity and space.
Topics covered in the video:
How to clean vocal channels using band-pass equalisation
Ducking reverbs using the s/c of a compressor
Side-chain compression on effects and how to set it up
Filtering for optimum clarity and cleanliness
Peak versus RMS selection for the compressor mode
Bleeding reverbs and how to control them