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Mid Side Processing In Mastering:
Why Some Engineers Won’t Do It

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Some engineers won’t do mid side processing in mastering.

I understand why. I’ll even tell you here.

But I’ll also tell you what I do to master successfully in mid-side only if and when it's needed.

I’m Giving You Info...

To help you be better grounded. To help you make better mixing decisions. It’ll be fun too!

Let’s do a quick review first (I refer to this as mid-side ‘in place’):

We get the MID element by panning the left and right channels of a stereo file to the center, summing to mono.

Mid Channel In Place

We place this result on the first track of an empty new DAW project.

We get the SIDE element by inverting the polarity of one of the channels first (on another copy of that same stereo file), and then panning everything to the center. On this composite signal we invert the polarity of one channel.


Polarity Invert
Side In Place

...followed by...

Polarity Invert

We place this result in the second track lane of the DAW project.

This Next Point Is Key

It's absolutely critical the MID and SIDE elements line up exactly and precisely with each other and be in perfect sync right down to the smallest sample.

This is an extremely important detail. This is so the file plays back with its original stereo image integrity.

If you understand this, then...

Now The Fun Part!

Let's take one of those hollow, offbeat, ping-pong stereo mixes from the '60's – you know with drums right, vocals left, that sort of thing (I love the Beatles, by the way, but NOT their stereo mixes!)...

Taxman - Edited Original

- and set it up as described above. But now I’m going to ignore that extremely important detail about staying in perfect sync. I’ll delay the SIDE element of the mix by 10 milliseconds!

Now when you play back and listen...

Taxman - Side Delayed 10 Milliseconds’ll hear a fuller, wider, and more centred mix.

Listen again more closely. You notice, however, you won't get any specific instrument placement: You hear the entire mix in the phantom center; and the instruments originally placed left and right are spread across the stereo field in a "wash".

You can do the same with a perfectly good mix of course. But the result will definitely not be perfectly good! No one would ever do this trick for a final master.

Now try to hear what happens when the shift is more subtle...

Taxman - Side Delayed 20 Microseconds

This is an example of what happens when the side component is shifted by a mere 20 microseconds. The high's are shifted ever so slightly to the center. On this mix the effect is of the tambourine sounding as it's been shifted slightly to the center. Also the bass has less bite: the pick harmonics also get shifted to the center creating alignment problems introduced by the subtle shift.

Play it a couple of times. Then play back the original for reference.

All this experimenting I’ve discussed finally leads to me tell you…

Why Some Engineers Won’t Do Mid Side Processing In Mastering

What we’ve been demonstrating with these delays is what I refer to as the DE-CORRELATION OF THE MID and SIDE elements. If these play back in anything but perfect sync, you'll lose the integrity of any imaging or localization in the mix. Even if it’s only by a sample! At 44.1kHz, that’s only 22 millionths of a second…


Analog hardware and modellings introduce phase nonlinearities. That's their nature. This means parts of the frequency spectrum may be delayed a few microseconds at its output compared to its input. If a file is treated in mid side mode with a component like this, the integrity of the image will be compromised. The severity will depend, to an extent, on the music file itself.

What’s The Solution?


Don’t use mid side processing in mastering. Bring me a mix where you’ve taken care of panning everything just where you want, with the space you want, and with everything focused how you want.

"How do I do that easily?"

There's a simple process I describe here that's free and easy to use.

"But what if there's just no more time for a remix - what happens then?"

If I have to use mid side processing in mastering, then I have use to a pure, transparent, linear-phase process. This way we ensure the integrity of the stereo image of your mix.

Mid Side is something you definitely do NOT want done in classic analog mode. Unless you want to it sound like those hollow, offbeat, ping-pong ‘60’s mixes!!

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