Mid/Side processing

I’ve come across this recently. I knew it was a recording technique until recently, when I discovered various plugins, such as M/S EQs, M/S Compressors etc. This post will cover the latter.

A good guideline was uploaded by Blue Cat Audio.

So what is M/S, what’s it good for and should you use it.

Let’s say you have a stereo signal. You want to enhance the stereo width without affecting the way your signal sounds in mono (this being regarded by some as a good indicator of correlation). With various short delays, you’re certain to succeed but may lose quality when listening in mono. This is where Mid/Side processing comes along.

The basic idea behind it all is this: you turn your stereo track into a Mid track and a Side track, hence the name. I think words don’t cover the concept as good as this:

Now you have two mono tracks which you can process separately. Notice that the Side cancels out if the master is to be converted into mono, thus preserving mono integrity. After you’ve processed these, you can turn them back into a single stereo signal just as simple:

(Thanks to hydrogenaudio for the schematics.)

As you can see, Mid/Side processing can be achieved in any DAW with basic I/O routing. You’ll probably wonder why are there dedicated M/S EQs and dynamics processors? Well, these plugins convert your stereo signal, process it and convert it back into stereo, thus being a lot faster and more convenient. But remember, Mid/Side processing is a technique, not a plugin.

Should you use M/S processing when submixing or mastering? It depends on the project. There is no definitive answer and no final technique for making something sound good, wide, narrow etc. You can always experiment with different approaches until you find the one that suits you best.

If you want to get started on M/S, you should try Voxengo’s MSED. It’s free!