Splitting out your stereo signals into separate Mid and Sides tracks can open up a world of creative options in your mix.
In this article I'll take you through some cool but simple Mid-Sides techniques that add space, colour and interest to your tracks or overcome common mixing challenges. Now, I realise that some of you regard Mid-Sides (M‑S) processing as powerful voodoo that's best avoided, so I'll make everything really easy to follow. While some simple maths can explain the conversion between left-right (L‑R) stereo and M‑S stereo, you won't need it here (though if you do want to know more, check out Hugh Robjohns' explanation: https://sosm.ag/mid-sides-explainer). All you really need to understand is that the Mid signal is what you hear when you fold your stereo mix down to mono, and the Sides is everything else — any frequencies in the left or right channels that disappear in mono.
Converting L‑R to M‑S and back to L‑R again is a breeze: all you need is an M‑S encoding/decoding plug-in. Your DAW may include one, but cross-platform options are available from Blue Cat Audio, Melda Audio, Goodhertz, and DDMF, amongst others. I've used Voxengo's excellent freeware MSED here.
You'll find a ZIP file of hi-res WAV audio clips for each of the step-by-step exercises in the right-hand Media sidebar on this web page; feel free to download these source files and work through the exercises in your own DAW, or just to listen to the clips of the results. [The SoundCloud MP3 examples embedded in this article are purely for instant auditioning purposes.]
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For most creative M‑S processing I like to split the original L‑R source out to two tracks in my DAW (I've used Cubase here but it works in any DAW). This allows me to process the M and S components of the signal independently, and a quick glance at the mixer makes it obvious what's going on. I can throw whatever processing I want at either the Mid or the Sides only, and can send the results anywhere else in the DAW. As you'll see, this opens up some wonderfully creative options. I suggest you save my routing matrix as a template in your DAW:
- Open a blank project and create a stereo track, which will host the original stereo file you want to process.
- Disable this track's master-bus routing (eg. in Cubase, change it from 'Stereo Out' to 'No Bus'); you don't want to hear this track in your mix.
- Create two stereo effects tracks/busses, naming one track 'Mid' and the other 'Sides', and use your source track's aux send facility (at unity gain) to route the signal to both of these tracks.
- Insert MSED as the first effect in both the Mid and Sides tracks.
- In the Mid track's MSED, mute the Sides, so that only the Mid component passes through.
- In the Sides track's MSED, mute the Mid, so only the Sides signal passes through.
And that's it: the track for the original stereo source is now split into separate Mid and Sides tracks. You can apply any effect or process to the Mid or Sides tracks, or to both, and it's all summed back to L‑R at the master stereo bus so you can hear the result normally. You can also balance the M and S components to taste by altering the Mid or Sides track's level in various ways: using the DAW's track gain or fader controls; using the gain knob in the relevant MSED instance; or changing the original stereo track's send levels. To me it makes the most sense to use the gains on MSED, as you can then do all your M‑S work (muting, balancing etc) in one place, and it's easier to use the matrix as a template for other sources you want to process.
Our first technique provides the basis for several that follow — by processing only the Sides component of a stereo drum loop, we'll create a cool shuffle effect to add interest. Import the stereo file 'drum-beat-104.WAV' to the first stereo track (the source track in your matrix) and name the track accordingly. If you want to use a different file that's fine, but note that for M‑S techniques you must start with a genuinely stereo file featuring different L and R signals — a dual–mono signal saved as a stereo file won't work.
Insert a delay plug-in after MSED on the Sides track (I've used Waves H-Delay, but any stereo delay is fine). Set the DAW tempo to match the file (104 bpm), and the delay to 100 percent wet and a straight 1/8 tempo-sync'ed delay, with very little feedback. On playback, this should combine with the dry Mid signal to create a lovely shuffling type...