Mid/side (or m/s) processing is a technique that i use in almost all my tracks. it’s pretty simple to set up in ableton live and you can get stunning results that are otherwise impossible to achieve. i’ve always thought it was pretty standard, but when i show it to people, i often get looks as if i pulled something from an ancient audio alchemist’s handbook. not quite so.
first a bit of theory: the difference between mono and stereo is that in a mono signal, the left and right signals are identical, and in a stereo signal they are different. the familiar way to encode stereo signals is to make a left and a right signal. but there’s another way: m/s encoding. m/s also consists of 2 signals, but they are called mid and side. the mid signal contains all the signal that left and right have in common. and the side signal contains everything that is different between left and right.
m/s encoding is quite common, for instance in the stereo audio on vinyl records. the left-right movement of the needle describes the mid signal and the up-down movement describes the side signal. this is decoded to l/r before the signal leaves your turntable.
and now the practice: in live there’s an easy way to turn l/r into m/s. if you set the width of the utility effect to 0% you get the mid signal, setting it to 200% gives you the side signal. all that’s left to do, is insert these in seperate chains in an audio effect rack to use them in parallel.
but the of course you have to do some processing to either the mid or side signal to take advantage of m/s. an example is to put a hpf on the side signal. this will remove the stereo part from your bass, making it mono. this can focus the bass and is essential when doing stuff for vinyl, which has a hard time handling stereo bass.
but you can get more creative. you can make any frequency less stereo by cutting that frequency in the side signal. boosting frequencies in your side signal makes your signal wider at those frequencies. and a wider track can also be achieved by compressing the whole side signal. be careful and use your ears, because your mix can easily become too wide and loose coherence. here’s a rack i use a lot on my master channel. it features a high-pass filter and a compressor in the side signal.
but you don’t necessarily have to apply m/s processing to the whole mix. imagine having a stereo clap. encode it as m/s and only apply reverb to the side signal. you can get a pretty big reverb without drowning the clap and losing the impact. you can find that rack here. try applying the same reverb on the l/r stereo clap. the difference will surprise you.
for those who don’t work in ableton live, voxengo makes a good free m/s encoder/decoder that can give you the same results. it’s a bit more elaborate to set up and you have to explicitly decode the signal back to l/r again after processing.
just bear in mind that m/s encoding in itself is not an effect. but what makes m/s processing so interesting, is that you can split your signal in unusual parts, process those parts with effects, and then put the signal back together. and there are other useful ways to split your signal, about which i will talk in future posts.