When I first heard about Mid/Side processing I have to say I was a little confused. I mean it’s difficult enough dealing with LCR mixing; Mid/Side added a new layer of complexity.
But then it came to me pretty quickly: if I am treating my mixes correctly, why wouldn’t I want to take advantage of processing my Mid and Sides differently. Especially during the Mastering stage.
STEREO
When I think of Stereo, I usually think of headphones. My left side is definitely different from my right, And only headphones can give you this binaural, detailed separation. But of course your reference speakers can separate as well. Just not like headphones which in reality are a drastic form of stereo.
From your reference speakers, however, you should be able to distinguish when something is in the center or the sides. If you split a signal properly, the stereo effect is marked, it is not difficult to detect. But split something in stereo incorrectly, and you can end-up in the same place where you started.
Conversely, if you are mixing everything to a Mono signal, you are only dealing with the Center. Switching a stereo mix to mono, everything is stacked on top of each other, nothing really stands-out. There is a reason why mono is lifeless.
So when we consider the domains of Stereo, we are don't only ealing with essentially the Center (Mid) and L/R (Sides), but a factor that many listeners take for granted, and need to be reminded constantly why stereo is such an incredible tool for making a mix 3D!
But there are a lot of variations of stereo we consider in our mixing. Especially depending on the genre or number of tracks.
I recently mixed a project that had four tracks. And I know what you are thinking, wow that sounds easy! But it’s far from easy when you consider the guitar, fiddle, and two vocal tracks - main and backup - needed to fill the entire stereo spectrum to actually sound stereo! Granted, the genre of the music was also very stripped-down, Red Dirt Country, so adding a bunch of effects and stereo panning wasn’t going to work.
And isolating a fiddle to 100% left and a rhythm guitar to 100% right wasn’t going to work either. It would sound very binaural and separated. If I were watching a three piece band on a small stage, I wouldn’t expect that kind of separation.
So instead of effect trickery or layered tracks, I used simple panning, some stereo reverbs, and stereo sends from the original tracks to broaden the stereo field when it was needed. This opened-up the stereo field when I didn't need it to sound intimate.
Long story short, I took what was a very mono type recording and made it broad but natural. You can hear the reverb when it is taken away abruptly but it isn’t distinguishable in the mix. The same with my stereo sends. Taking a mono track and sending it to a stereo Aux and then bringing it up and down in the mix, when needed, allowed me to create a ton of dynamic while still keeping with the simple presentation.
And finally, the panning I employed was very simple. For most of the project, the fiddle was 25% left while the guitar was 25% right. The vocals dead center. When the guitar was on its own, it was panned dead center as well.
So even within a very basic song I was able to incorporate a lot of dynamic and take full advantage of the stereo field.
Normally we aren’t dealing with such such a simple project. I typically see 20-50 tracks, sends/Aux channels, etc., and at that rate, things start to pile-up. The stereo field becomes saturated.
So how can we take a fairly complex project and bump it up a level more? Allow the stereo field to shine while maintaining the original intent of your panning and EQ moves? By giving the entire stereo spectrum an even more surgical treatment.
MID/SIDE
Many people first experience Mid/Side (MS) during Mastering. Most Master Engineers will treat the Mid differently than the Sides because in most mixes, panning usually designates specific instruments live within a certain part of the stereo field.
Consider a basic rock song with dual guitars, bass, drums, and a vocalist. It’s pretty guaranteed you will keep bass and vocals down the middle, and especially drums. Of course we are not talking about drum room mics or overheads which tend to be panned to the sides.
And it’s also a good bet you will pan the dual guitars left and right. How far depends on your style. For me, it’s always 100% L/R.
In addition, you will probably pan a lot of effects to the sides like vocal or drum reverb and delays. Even backing vocals. But the main center instruments will still dominate the Mid, while the guitars will dominate the Sides.
So now that we have a good example of a basic setup, with standard Mid and Side sources, we can move-onto understanding them better.
MID & SIDE FREQUENCIES
Let’s start with a comparison of the frequencies in the Mid and Side.
Low-End Frequencies - Remember we identified that most of the low frequency instruments like bass and kick/snare/toms are in the center; compared to the sides which have guitars and maybe some wide stereo effects from the center sources. We can now confidently apply some bias to the Mid, giving it more bass, and conversely, potentially remove unnecessary bass from the sides.
Midrange Frequencies - Separating the guitars from the vocals through panning, we can also bias certain midrange frequencies in the Mid; frequencies that are different from the guitars. Panning two instruments who share a lot of the same frequency space not only allows us hear each of them better, we can treat them better in MS processing as well.
High-End Frequencies - Any high-end information in the Mid will tend to be cymbals - if you have not panned all of them - and vocal air (frequencies generally above 10k that give the vocal a lot of shimmer). That and some high-end snare information. When we are talking about guitars, there could be a lot of overlap with the center instruments in the high-end depending on the genre. Loud distorted and crunchy guitars contain a lot of high-end information, so our ability to bias the high-end for mid or side will be somewhat limited. But there are still opportunities as we will discuss.
PROCESSING MID & SIDES
I recommend you perform these moves on an EQ around the top of your Master FX chain in order to hear the full effect of the changes I am going to recommend. But first a note about Mastering.
When dealing with individual tracks, it is not uncommon for me to add or remove 3-6dB from a source in one or many frequency bands. This is just part of the mixing process. But a 6dB anything in the Master is pretty dramatic. Remember we are dealing with the entire mix here, and you have already done a lot of work to get to this point.
Keeping this in mind, I usually limit my EQ moves on the master to 1-2dB, except for filters which we will discuss in a minute. Maybe I will hit one or two 3dB gains or cuts if I can get away with it. But if I find I am making 3dB or more changes all over the spectrum, I am not ready to master.
So here are some of the moves I generally start using by default when I throw my Master EQ on a project.
First you will need an EQ capable of mixing MS. I use the EQ Sitral by Arturia for my Masters. The curves are fantastic and the control is very subtle. But you can use just about any EQ that has this capability. Here is a look at my default M/S preset, which is where I start, but usually end-up somewhere a little different:
Second, make any changes to the master in the full mix. Soloing the Left or Right, or Mid is just a recipe for disaster in my experience.
So here is where I start:
Low-End - Cut the lows starting around 100hz from the Sides with a gentle high-pass filter. This will remove unnecessary low-end from the Sides which typically do not contain a lot of this information anyway. The Sitral tends to pull the mids down as well when I do this, but the overall effect is gentle when smooth curves are applied.
You can also add ~2dB to the low-end on the Mid using a shelf starting around 10hz. You are now boosting what you subtracted from the Sides. In my default EQ I don't add low-end, but will make-up for it if needed.
Try placing a gentle filter on your Mid around 50hz that ends around 20hz to tame any sub frequencies. Depending on the genre, you may find this is unnecessary but you would be amazed how much it brings-out low-end frequencies just above the cut!
Midrange - When it comes to treating Midrange, I generally prefer the Sides to be a little stronger in the upper midrange (1k-10khz), while my Mid tends to be stronger in the lower mids (100-1khz).
For the Mid, which is where the vocals will sit, you will find voices tend to shine in the 1-3khz bands, but even have a lot of information between 3k-10khz. A stronger Side in the upper mids will allow the panned harmonies and vocal effects to pop-out even more.
On the Sides, Guitars - or synths for that matter - that are panned will have a lot of upper midrange information as well. This slight boost will give them separation in the mix. The slight cut in the lower mids for these instruments will also allow the Mid instruments like drums and bass to shine. Thereby creating even more separation from the Sides.
Midrange is a tricky area because so many instrument live there. So keep your moves conservative. Remember the instruments that live in the Mid and Sides will benefit from moves that enhance their position.
High-End - It is pretty crazy how 1-2dB of boost or cut will impact 10-20k, especially when you are biasing the Side over the Mid.
Generally I will boost my Sides by ~2dB over my Mid. This allows the sides to sparkle a little more, especially against any effects you hard-panned like reverbs and delays or backing vocals.
I may even insert a gentle high-cut filter on the Sides starting around 15k and have it end at 20k. This is similar to the low-cut filter we added to the Sides. This will tame any crispness in the Sides due to the boost and allow the Mid to sparkle more.
CLOSING THOUGHTS
Once you setup your basic template, save it as a preset or the default for your Master EQ. This will save you a lot of time.
Also, mix into your Master EQ. Don’t wait until the end to apply it. Start with the default as we discussed above and then once you are ready to master you may find you are 90% there already.
The same goes for Limiting, Saturation, or anything else you would normally put on your Master FX chain. Mix into settings that will generally work until you are ready to master your project (e.g., ~3-6dB boost on your Master Limiter).
If your EQ has the ability to reduce its range to +/-6dB, use it to keep your moves conservative. You want this EQ to look different from your mixing EQ; it needs to keep your eyes in check.
I will also employ a nice feature in EQ-Sitral that reduces the size of my moves. So when I take 3dB off a dial, it’s actually only applying 1.5dB. This allows me to depend on my ears more and less on the numbers. And it decreases the sensitivity of the dials. Pretty genius!
Auto-gain is another feature EQ-Sitral has that I will use frequently. Since we are dealing with very small changes here, it may not be really necessary. I generally recommend auto-gain for EQs in mixing and mastering so your ears won’t get fooled by loudness changes.
If you find yourself digging into your tracks while mastering, you are probably not ready to master. Which is fine. The more you learn about MS processing, and mastering, the more you will keep these things in mind as you mix. Just try not to mix and master at the same time.
When you are ready to test the changes you are making to the EQ, do a lot of A/B referencing. Turn off your changes and then back on. You should be able to hear the difference. If not, push the change harder so you can hear what to listen for, but then dial it back to its original point. You may find 3dB or just 1dB is preferable. Just use your ears and try not to depend on the spectrum analyzer which isn’t really showing you anything useful.
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