Mid-Side (MS) Mixing Techniques: EQ & Compression
So what is mid-side processing? A simple way to think about mid-side processing is to consider a stereo audio track. In a stereo audio track you have two channels: you have a left channel and a right channel. So you might have some signals that are on the left channel and when they’re presented through a stereo set of speakers or headphones, the signals on the left channel are presented through the left speaker. The signals on the right channel are gonna be presented through the right speaker. A different way to think about a stereo audio track is to consider that there are signals that are gonna be presented to both speakers at the same time. When those signals are presented to both speakers they’re perceived by a listener as coming from the center, or between the speakers. Or actually, the middle of the stereo field. That’s where the term mid channel comes from.
So when you’re doing processing, what you can do is group together all the signals that are gonna be presented to both speakers at the same time, and you can process just those signals separately. On the other hand, when you have signals that are not presented to both speakers at the same time — maybe there’s some that are just on the left and some that are on the right — you can group those signals together and put them on a different channel called the side channel, then you can process those signals separately.
So there are some typical places where you would want to use mid-side processing when you’re mixing. Most obvious place is the master buss. The reason for this is by the time all your signals are summed together on the master buss, you typically have everything balanced from left to right in the stereo field. You have some information on the left, and some information on the right. And some instruments in the center. So you pretty much have things balanced. You might have the kick drum in the center, the bass guitar in the center and the snare drum in the center. Then you have things like maybe some of the other instruments — guitars, cymbals — things like that on the sides.
So, what you want to do is consider how you would process these signals separately. I’m gonna bring up an equalizer to begin with and show you how this works. So this is the IK-Multimedia T-Racks equalizer. It’s a good one to use because it let’s you switch between the left/right kind of processing and the mid/side kind of processing. So let me should you what this is all about. I’ll play you back my song that I’ve got going right now, just with some drums, bass guitar, electric guitar, an acoustic guitar and a little bit of piano so you can hear what’s going on. Then I’ll talk about how I’m gonna process it.
So right now when you bring up the equalizer, you have the left channel and the right channel grouped together. So whatever changes I make here to the equalizer, they’re gonna happen to both the left channel and the right channel together. Now, what you can do with this is separate the left channel and right channel and process them separately so you can make changes just to the right channel or just to the left channel. I’ll quickly demonstrate that just by using this low cut filter.
So here I’m just affecting the right channel by rolling out the low frequencies. What you can do then is switch to the mid-side processing where you have two channels now. You have all the signals that are gonna be presented to both speakers in the mid channel. Then you have all the signals that are not gonna be presented to both speakers — just the left channel or just the right channel — and they are grouped together on the side channel over here.
So just like before, I can show you — demonstrate how this sounds.
What I’ll also do here is, you can control the output level separately, so I’ll just pull out the mid. Now all you’re hearing is the side. Or I can do the other way around. Just hear the middle. So this by itself just with the output gain control can be used if you want to turn up all the signals in the center, for instance like if you have the vocals or the drums in the center, and you want those to be louder than what’s going on on the sides. Or the other way around depending on your mix, you may decide at this point in your mixing stage that you want to do is turn up the things on the side, and bring down what’s in the center whether that be the vocals or drums or anything like that. So I’ll just show you some typical things you might do, for instance if you want to bring the drums up.
Just with a couple dB boosting in the center and pulling out on the side, I’m able to increase the level of the drums.
Alright, so what are some other, more complicated equalization techniques that you can use with mid-side processing. A common one is the fact that you have a lot of the bass instruments, that are panned to the center like your bass guitar and your kick drum, those are typically in the center — what you might want to do is roll out the low frequencies that are in the side channel. What that’s gonna do is make sure all the bass instruments are focused in the center.
Another thing I like to do is, especially with the side channels, a lot of times the cymbals can sound a little bit harsh. And what you can do is just use a peak filter here to back off some of the harshness in the cymbals. So what I’ll do is back off first here the sound in the center and just focus on what’s on the outside in the side channel, and then equalize that and bring the middle back in.
Should’ve been working on the side one. I’m just backing off a few dB so my cymbals are less harsh. I’ll bring back the center.
Alright, now let me talk about some mid side compression techniques. So I’m gonna use the T-Racks vintage compressor, which is based on the fairchild compressor. And the thing with it is you can either compress the left and the right, compress everything together, or you can switch into the mid-side like this and do them separately. So, without, just in the typical linked mode, this is what you can do. Dial in compression. Let’s see how the compressor operated together. Or you can switch to lateral vertical or mid-side, process them separately now. Bring down the sides, just the center here. Just the sides now.
So typically what you might want to do, compressing the master buss, is squash more what’s going on in the center — that’s like your snare drum, your kick drum, your bass — things like that, with the faster time constant to really squash the attack. And then with the sides, you might want to use a slower time constant, slower attack, slower release, and a few dB — maybe just kiss the gain reduction here — but get it more pumping on the center. So let’s just experiment with that.
That’s it. I hope you guys had an opportunity to learn some more about mid-side processing and see some conventional techniques you might use on the master buss.