What Exactly Is Mid/Side Mixing?

Mid/side is becoming a much more common term in the studio these days. While it used to be something used exclusively by tracking engineers recording in stereo, today it’s capable of completely changing the way mixers work with tracks in their session. 

Mid/side mixing effectively allows us to kill two birds with one stone – mixing the center (or mid) of our tracks one way while mixing the left/right “sides” in a completely different way. The strategies can often go in two different directions or act as a way to reinforce one another with minimal effort, but above all else, mid/side mixing gives you flexibility.

Let’s take a look at how home studio enthusiasts and industry professionals are using mid/side in their studios today.

Mid/Side Recording 

As I mentioned, mid/side originated with techniques made famous by recording engineers, not mixers.

Nearly 100 years ago, engineers found that the process of recording a sound with a mid/side microphone placement resulted in fuller, more detailed audio. The technique was developed to capture sounds in a similar manner to how humans hear them. It takes full advantage of two microphones without technically qualifying as a “stereo” miking technique.

So if it isn’t stereo – what is it?

The core concept of a mid/side microphone configuration has everything to do with the polar patterns of the microphones you choose and a perfect 90-degree angle between them to get that “human-like” characteristic.

A mid/side mic setup is actually very straightforward: 

1. Point a microphone with a cardioid polar pattern directly at your audio source. This will be your “mid”.
2. Place a microphone with a figure-8 polar pattern at a 90-degree angle from the first mic. This will be your “side”. It’s best to keep the ribbon or capsule of this microphone as close as possible to the original mic to maintain good phase correlation.
3. In the box, create a duplicate track for the figure-8 microphone. Pan the original track hard left and the duplicate hard right.
4. Keep the cardioid mic panned center.
5. Adjust levels to taste. Many engineers will group the two figure-8 (side) tracks together so that they’re always set to the same level as the other. Once you’ve found a good balance, you can even add the cardioid (mid) track to the group and raise/lower all three without breaking their balance.

Using this technique, the figure-8 polar pattern is acting as a super-wide stereo mic might. It’s picking up sounds from both sides of the microphone and when you duplicate it and pan one the opposite way, you get a wider sounding track than you might otherwise record. The cardioid mic in the middle fills in the center with the more direct soundwaves – transients and other characteristics that the figure-8 mic might not capture as well. It adds directionality to the source.

Most importantly, you can treat the content captured by the mid mic completely independently from the sides and vice versa.

The Case for Mid/Side Mixing

Even if you don’t have the pleasure of capturing your audio with a mid/side mic setup, that doesn’t mean you can’t take advantage of the same concepts in-the-box. Many digital processors and plugins today offer some level of mid/side support.

But why do you need it in the first place?

The idea behind mid/side mixing is that you want to create a level of separation between the center (middle) of your audio and the edges (sides). There is no hard cutoff line where something becomes inherently one of the other, especially since mono sources panned to the center are still playing back through two speakers.

With traditional EQ and compression, you’re working with your audio in a very broadband application. Regardless of the source being mono or stereo, you’re often applying your tonal adjustments to the full signal. An EQ boost applies to the whole spatial field – fine for many use cases, but not always the perfect solution.

Mid/Side Mixing Explained

When a plugin gives you mid/side functionality, it completely solves this problem. You’re able to treat the edges of your track one way and the center of that track another. Mono, stereo… it doesn’t matter.

These plugins are really running two processes at once – one to treat what they’ve defined as the center (mid) of the audio and one to treat the sides. Working in this way, mixers can make complimentary moves without any complex routing. They gain twice as many controls in a single plugin instance, and the applications are endless.

A common use for mid/side mixing is to use EQ to boost a frequency in the center while simultaneously cutting that frequency from the sides. This results in a more pronounced adjustment, adding last accuracy to the positioning of at least that frequency band.

Another common use is to apply a compressor to something like a guitar bus for the same benefits. Mixers can use a single compressor to heavily compress the center of their rhythm guitar mix while setting the ratio lower on the sides. Not only does this make the rhythms appear to sound wider, but it perfectly tames any dynamic peaks that might overlap the lead vocals while keeping things sounding dynamic and punchy on the sides.

Living In A Stereo World

When mid/side recording was first introduced to the audio world, I’m sure they never saw the future applications coming. The technique was a way to “fake” a stereo sound on audio that would likely be heard in mono. Hi-fi systems didn’t show up until decades after the first use of the technique. 

But today, there’s no excuse for having a poor stereo mix. Spatial wideners and mid/side processors have enabled us to create more immersive audio experiences than ever, and the biggest and best mixers are taking advantage of the benefits they offer.

Are you ready to start using them too?