Exploring the Power and Use Case Potential of Mid-Side EQ Processing

Mid-Side EQ is a special type of EQ which allows you to equalise the mid (centre portions of the stereo field) and the sides (left and right together) portions of the field independently of one another. It is known for its applications in Mastering, however, there are several use cases which I commonly gravitate towards in mixing and sound design.

Number one: Side rumble reduction.

A pet peeve of mine is having excessive bass frequencies in the far left or right of a stereo field when listening back over headphones. This isn’t a problem which bothers me when listening over speakers, but listening over headphones is a different story. There is a scientific reason for why it bothers me, which is that is that in real life, it is practically impossible to experience excessive bass in one ear and not the other! Due to the way in which low frequencies (which have very long wavelengths) wrap and diffract around one’s head, if a bass frequency is travelling from the left direction, it will be heard in both ears.

This is the reason why I think hearing bass frequencies on one side of the headphones only is a very unnatural experience.

The example I am going to use is the Fabfilter Pro Q Equaliser, but of course, Mid-Side EQ functionality is offered in many different products!

As you can see in the image, this low shelf that I have created has been side-to-side mode. Meaning that only signal in the far left or far right of the stereo spectrum will have this low shelf applied to it.

The result of this is that bass frequencies are left in the centre of the field, and bass is reduced in the sides, which aligns more with the real-world experience of being exposed to bass frequencies.

Number Two: Faking stereo movement from a mono file

We all know by now (and if you don’t you will in 5 seconds) that taking a mono sound and applying panning automation does not mimic real movement captured with a stereo pair of microphones. And while this technique isn’t a true substitute for the real thing, I have managed to achieve some pleasing results.

The technique is as follows:

Put the sound on a mono track in your DAW.

Route the sound into a stereo auxiliary track.

Put our favourite Mid-Side EQ on the auxiliary, with a very similar curve setup to the previous example; one that attenuates bass in the Sides only.

On the mono track, apply panning automation to move the sound.

The result is that the movement will be greatly softened, but movement will still be evident!

If we think about how a similar movement might have occured in the real world and subsequently captured over a stereo pair of microphones, it is largely the mid and high frequencies that capture the greatest differences between left and right microphones. The bass frequencies are mostly the same and void of movement. In this way, our technique of reducing the ‘movement’ in the bass frequencies while allowing the movement in the higher frequencies mimics real-world stereo microphone behaviour.

So there you have it! Two interesting uses of Mid-Side processing that you may not have come across before.