Null test

Every so often you will come across a situation where you need to know whether two pieces of audio are the same, or whether they're different. 

Maybe you have two mixes of the same song, and you're like 99% sure that they sound the same. But you're not 100% sure. And you're worried that one of them sounds better than the other, and you need to know.

So how do you know for certain whether they're actually the same?

You do a null test!

A null test is the definitive way to see whether two pieces of audio are identical. And it’s super easy to do.

The way you do it is you drag both files into your DAW, and you get them exactly time-aligned with each other on two adjacent tracks. Zoom in to the sample level and make sure the waveforms are precisely aligned.

And then, flip the polarity on one of the two tracks, with a Trim or Gain plugin. (The polarity button is the one that looks like a Danish Ø, with a line through it. Polarity is also sometimes referred to as phase, which is inaccurate, because they are different things. But even audio manufacturers sometimes do it, so ¯\_(ツ)_/¯.)

What flipping the polarity does is it inverts the waveform — flips it upside down.

If the two pieces of audio are identical, the inverted waveform on the one track will exactly cancel out the non-inverted waveform on the other track ... and you'll hear nothing but silence! 

And if the two pieces of audio are different in any way, the waveforms won't precisely cancel out, and what you'll hear is what's different between them — which can also be very helpful.

Flipping out — jamie