Mid/Side processing is a technique many mastering engineers are using because it is so easy and effective. But it’s not for mastering proposes only, you can uses these techniques on any STEREO signal.

How Mid/Side processing works

A STEREO signal contains 2 signals, left and right, but a Mid/Side processor splits the signal into 2 different MONO signals, not left and right but:

• A MONO signal called Mid (read: middle) containing the frequencies which are played at the same volume level in both speakers, left and right, at exactly the same time. In other words: these are identical frequencies for both speakers.
• A MONO signal called Side containing the frequencies which are out-of-phase with each other when you compare the left with the right. In other words: frequencies which are only happening in one speaker at a certain time and not at all in the other speaker.

These 2 MONO signals can be processed by using EQ, compression or other effects. When sending these processed signals back into the Mid/Side processor, these Mid/Side signals will be converted back into the original left and right signal.

A Mid/Side processor is a very simple device. It doesn’t change the signal but only uses phase reversing techniques to “filter” out the same sounding frequencies (Mid) and the opposite frequencies (Side).

Example: Frank Ocean’s Pink + White

Check out the example I made using Frank Ocean’s Pink + White:

The first couple of bars are unprocessed, then you’ll hear the Mid only part (both left and right are playing exactly the same frequencies at the same time and at the same volume level) and next you’ll hear the Side only part (both left and right are playing total opposite frequencies: an out-of-phase sound).

And notice how at SoundCloud the graphic waveform for this track is showing a huge cap. That’s the part where the waveform is very small, where the Side part is played. This shows us the way SoundCloud’s graphic convertor works: it sums both left and right channels. So if both signals are very out-of-phase sounding the waveform will look as if almost nothing is happening in your track. Which is absolutely not the case at all… Many spectrum analysers can fool you in exactly the same way by the way, so always be aware!

Why is this so cool?

With Mid/Side you can process the mono sounding part (Mid part) and the ultra wide, out-of-phase sound (Side part) independently from each other. For example you can filter/EQ the lower frequencies out of the Side signal. Super low frequencies are directionless and therefore it makes no sense if you pan them to the left or right, you ears will simply not notice them coming from those directions. Using Mid/Side processing you can adjust things you won’t be able to adjust with simple panning. You can of course also change the balance between the Mid and Side levels, making the sound either more MONO or Wider. Super simple but cool.

Try using compression only on the Mid part and leave the Side very dynamic. You can get a great sound this way. And because the Mid and Side parts are MONO signals, you apply MONO effects to these 2 different sounding signals.

How to use Mid/Side techniques in Reason

In the Factory Sounds ReFill of Reason you can find a Mid-Side Mastering section with many out-of-box effects for Mid/Side processing. But you might as well download one of the free Rack Extension (RE) devices which makes it easy to split a STEREO signal into Mid/Side signals and which offers a lot of flexibility:

Anansi Mid Side Router

Download it for free: shop.propellerheads.se/product/anansi-mid-side-router/

Here’s a screenschot of the config I am using with 2 EQ devices, one for Mid and one for Side:

RE 181 Mid/Side Audio Converter

Download it for free: shop.propellerheads.se/product/re-181-midside-audio-converter/

Very cool right?