Today I Learned: UAD’s LUNA Doesn’t Natively Support Flipping The Phase Of A Recorded Track

I had a bit of a surprise today. I went into my current DAW – Universal Audio’s LUNA – to do something so basic, I took it for granted. Only it wasn’t there …


I’m learning to record my acoustic guitar using the mid/side technique. For this to work, I need to be able to flip the phase of a track after it has been recorded and copied.

I’m recording into Universal Audio’s LUNA DAW. At the time of writing, LUNA can only flip the phase of a track while the track is being recorded. This is a really basic feature, and it’s surprising that it is missing from LUNA.

The workaround is to use two additional plugins that support phase inverting on your side tracks. Unfortunately, these plugins consume precious DSP CPU, and they colour the sound too. Those are costs / consequences that you might find too expensive.

What Is “The Phase Of A Track”?

Any audio signal has two aspects: the positive signal, and the negative signal. An audio waveform switches from positive to negative and back again all the time.

When you’re dealing with just one audio signal, this normally isn’t important. As you start to combine two or more signals together, though, these positives and negatives start to interact.

When audio signals are “in phase”, the positives and the negatives are roughly rising and falling together, creating a stronger / louder signal. They re-enforce each other. When they are “out of phase”, the positive peaks of one signal are being (partially) cancelled out by the negative peaks from another signal.

Watch this video to see and hear it in action:

Why Does This Matter?

I’m taking advantage of the Christmas holidays to practice recording acoustic guitar.

To give me a lovely stereo effect with limited phasing issues, I’ve decided to use a mic’ing technique known as mid/side mic’ing. It’s a very forgiving technique; perfect for someone like me, who is both performer and their own sound engineer.

Here’s how it works:

  • Microphone A is a directional microphone of some kind. It captures the mid sound: the sound that will be at the centre of my stereo image.
  • Microphone B is a figure-of-8 microphone of some kind. It captures the side sound: the sound that will fill out the left and right of my stereo image.

Now, microphone B is still capturing a mono signal. To turn it into a stereo signal, I have to take a copy of the track, and then flip the phase on that copy. I pan the original track hard left, and I pan the copy hard right.

And hey presto: I have a stereo signal which I can then further enhance by using delays, reverb, and all sorts of other tricks. (That’s for another day.)

There’s plenty of videos about this technique on YouTube. I’ve picked this one out because it focuses on explaining how mid/side works:

If I can’t flip the phase of our copied track, I’m stuffed, and this technique won’t work.

I’m using Universal Audio’s LUNA DAW for my recordings. LUNA is aimed at – and heavily promoted by – serious professional engineers and producers. This is such a basic feature, it never occurred to me that it might be missing.

UAD LUNA Can’t Flip The Phase Of A Recorded Track

At first, I couldn’t believe it. There is a ‘phase invert’ button on each track in LUNA, after all. It’s right there, in the Input section of the track. I was expecting to simply click it, and job done.

Unfortunately, it’s only active during the initial recording of that track. Once the track has been recorded, that’s it: the phase button’s disabled (along with the rest of the Input section of the track).


Fortunately, there is a workaround, but it comes with a price or two …

An Expensive Workaround

The workaround is pretty simple: find a UAD plugin that has a phase button on it, and add it as the first insert on both of the side mic tracks (i.e. both the original track and on the copy). Then, on the copied track, go into the plugin and flip the phase.

To check that everything is working, pan both side mic tracks to the middle, and solo them both. You should hear complete silence, because both tracks should be cancelling each other out perfectly.

You can use the UAD-610-B preamp plugin to do this. It’s included for free with every UAD Apollo.

So what’s expensive? Well, two things:

  1. First off, no matter which UAD plugin you use to do this, that plugin is going to be adding additional colour to the sound. AFAIK, every single UAD plugin that has a ‘phase invert’ switch also colours the sound. That extra character might not suit your mix.
  2. Every UAD plugin uses precious DSP CPU. UAD plugins don’t run on your computer, they run on the DSP chip(s) inside your UAD interface.

Unfortunately, you can’t just use one plugin on the copied side mic track. You must use the same plugin on both side mic tracks – with the exact same settings, except for the phase inversion – otherwise you don’t get a perfect phase cancellation.

Your Apollo unit only has so much DSP CPU to go around, and if you’re already struggling to run all of the plugins that you want, having to use two more just to flip the phase on one track might well be the straw that breaks the camel’s back.

Final Thoughts

With LUNA, Universal Audio have moved from emulating classic outboard gear to emulating the entire recording studio. It’s an exciting – and enticing – prospect.

Along the way, they seem to have forgotten some of the basics. It’s been literally decades now since most people worked in a purely analogue workflow. LUNA needs to include features that we take for granted in digital workflows too.

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