For this tutorial we’re going to posit an example scenario: a way to achieve the common practice of narrowing the bass content of a stereo track by scooping out the S channel’s low end—but this time, using analog gear instead of plugins. But what if we don’t have any M/S gear? Not to worry.
All you need to accomplish this feat is an analog processor which has a low cut or low shelf filter (a hardware EQ, for example), Ableton Live, and an audio interface or soundcard suitable for routing 2 channels of audio out and back in.
Equipment with two (L, R) inputs (and outputs) is ideal, but you can use mono gear as well—that just requires a couple extra steps of setup.
No M-S Built in? That’s Fine. We’ll Do it Ourselves.
To get your gear to affect the M and S signals of your source audio which you’d like to process, first we have to re-encode the L-R signal to M-S.
Generally when this is done, the M signal then resides on the L channel and the S signal resides on the R channel. To accomplish this task, we’ll use the “MS to LR Controller” rack for Ableton Live, by yours truly, from the free pack Utilification. Just drop the rack in as-is and it will now have re-encoded the signal.
Because of the fact that you can control what gets sent to and from Ableton Live, it doesn’t matter if you don’t actually have any analog gear pre-loaded with mid-side capability. By using Ableton Live to alter the stereo matrix, we can send the S channel out re-encoded as the L channel, and the R channel re-encoded as the S channel. This way, we can process any stereo material in “M-S” mode rather than typical stereo L-R.
I’m not going to describe what Mid-Side processing is here for the sake of brevity, so if you don’t know, go look up a few articles on it then come back.
Now that the signal is hitting the gear, let’s implement our low-cut on the R channel. The gear calls it “R”—but we know that it’s secretly an “S” channel pretending to be an “R” channel.
But wait! There’s one more thing. If we forget, our audio is gonna smell funny and probably not in a good way. We have to decode our signal back to normal after it comes back to the DAW so that it comes out the speakers the way it’s supposed to. To do this, simply place an instance of “LR to MS Controller” after the External Audio Effect. What this does is take that L signal (aka “channel 1”) coming from the hardware and says “you are actually a center channel”, and take that S channel from the hardware (aka “channel 2”) and tell it “you are actually a sides channel”. Now that the channels have been reminded of what they are, we have the result that whatever processing we did to channel 1 with our analog gear applies to the center, and whatever we did to channel 2 applies to the sides.
So for example, you could enhance stereo width by boosting the highs of the S signal. Or…. narrow the bass by only cutting it from the S signal. Or perhaps boost the high-mid frequencies of the M channel and saturate it with a tube preamp for a more forward sound.
The next step is to actually send your audio to your gear. For this, use Ableton’s “External Audio Effect” plugin, because it’s designed for that exact purpose. Make sure to activate and route through the proper channels (which will vary according to your exact setup).
For attempting this processing mode with mono gear, what we’ll do instead is send the S signal to the gear while leaving the M channel untouched. You’ll want to record the S channel on a new track, remove all S information from the source track (with an instance of Utility, for example), then combine the two and adjust the timing carefully to minimize your phase offset, since it’s probably imperfect due to the hardware latency. Or, you could send both the isolated M and S channels to the gear separately, with different settings applied to each, then recombine them. This will solve the latency issue without any thought, since the same latency will have been applied to both tracks.
As an example, to achieve our originally stated goal of a low-cut on the sides channel, i would probably use a combination of 2, maybe 3 devices in my analog chain: perhaps the low-cut switch on the audio interface input preamps to chop everything below 80Hz, combined with a 120Hz low shelf dip of the Quintessence hardware EQ. By adjusting the combination of controls carefully, i can create a fine-tuned, custom curvature. By using before and after analysis, i can make sure that my pre and post signals are of the same overall energy, to avoid blunders based on the loudness illusion.
So… what piece(s) of hardware do you have that you can use to process the mid or sides only? Have you tried doing so on your own yet? Are you going to now?
One Word of Warning
Usually in a audio file, the L and R channels are of relatively similar loudnesses. However, in an M-S matrix, the M channel is generally quite a bit louder than the S channel (depending on the material, of course). Due to this fact, it’s a good idea to make sure there’s a bit of extra headroom to compensate for it and you may need to adjust your usual gainstaging slightly to ensure avoidance of clipping. This volume difference is also good to keep in mind if you are applying any subsequent stereo effects to the chain before it is decoded, as unlinked dynamic processes from things like compressors or gates may react quite differently to M-S than to L-R signals. You might need to boost the S channel’s input gain quite a bit extra in order to get a compressor’s threshold to start responding, for example, and doing so can amplify the noise floor, so you might want to then reduce the output volume afterwards as well.
Keeping Mindful – the Moral of M-S
I wrote this post with analog gear in mind, but keep in mind that this technique is not at all limited to the analog domain; you can use the MS / LR Controller racks to route any VST or AU plugin as Mid-Side instead of Left-Right. How cool is that?!? Unlike most M-S encoder/decoder plugins, performodule’s racks also allow you to encode the channels atypically if you prefer, so that L is the S channel and R is the M (you never know when this might be useful). You can also fine-tune the gains and pannings of the layers.
Want to use that favorite L-R compressor as an M-S compressor for a certain song? No problem! Once you realize how elementary and low-CPU these re-encodings are, you’ll wonder why all stereo plugins don’t have M-S functionality built-in. And you’ll also find yourself shaking your head a bit at plugin manufacturers who tout M-S functionality as some amazingly innovative thing. It’s neither new nor innovative nor difficult to implement—but it is indeed super nifty and fun and cool.
FREE M-S ENCODING & DECODING RACKS
Oh yeah…. here’s the link to Utilification, where you can acquire the aforementioned MS Controller racks for the massive price of $0.00. Enjoy!
NOTE: if you already possess the pack, please re-download and update it with the current version, as one gain value error was fixed.