This One Test Can Change How You Mix Audio

Hey friend, welcome back to another Sage Audio video.  Today were going to be discussing a topic that has major implications for mixing, mastering, and especially tracking – but what we’ll be primarily focusing on, is something called a Null test.  This test will help you to determine when two tracks are completely identical to one another, and just as importantly, it lets you hear the isolated differences between the two.

So, whether you’re just learning about phase relationships in audio, or already have some knowledge about the topic, I think this video will help to further that understanding, and will translate into better mix techniques, so I’m definitely excited to share this with you all.

But before I do, if this video or any of the other sage audio videos have been beneficial for you, please subscribe to the channel, or if you’ve already subscribed, click the link for notifications.  Also if you’re working on a mix, or if you’ve just finished one, and you’d like to hear what it would sound like professionally mastered, please send it to us at SageAudio.com and we’ll send you a free mastered sample of your work.

So what I have here are two tracks – both full mixes, both completely identical tracks.  The difference between the two is the phase. Now, what I mean by that is that the phase of one of the tracks has been inverted – so let me show you what that means.  If we take a look, you can see that the sound waves are the exact opposite of one another. You can see that when one wave goes up, the other goes down, in an equal and opposite manner.  Just for the sake of knowing them, the terms for these wave movements are compressions and rarefactions.

Because the waveforms are opposite, what we’ll have is complete phase cancellation when the tracks are played.  Essentially the sonic energy of one track is being negated by the sonic energy of the other, resulting in an energy free, or in our example, a sound free output.  

Although I doubt we’ll be able to hear anything in this example, let’s take a quick listen.

Now as you can see the tracks are clearly playing, and when observed individually they have signal, but when combined, there is absolutely no output.  

Let’s check out another example, in which I change the EQ of one of the tracks.  Notice that when one track is changed, the tracks are no longer opposite, and the new phase relationship results in only partial cancellation.  

This will be true in any instance where you change one of the tracks, be it a change in amplitude, saturation or distortion, temporality such as reverb or delay – whenever you change one track, you alter the phase relationship between the two, and in turn interrupt, so to speak, the phase cancellation.  When the two tracks are no longer completely and equally opposite to one another, they will no longer cancel each other out.

So let me show you how to accomplish this on your own, it’s very simple.  All you need is a phase inverter plugin – these are typically found in the utility section of your plugins.  Make sure to invert both the left and right side of your stereo signal. You can either experiment with this is real time, or you can bounce out the track, as a phase inverted track and import back into your session, as I did in our example here.  

So experiment with this process, this way you can determine if two tracks are identical, or different in some way, allowing you to hear what is specifically different between the two.  Keep in mind that some temporal plugins, or high CPU, latency inducing plugins will in turn change the timing of your track’s playback, which will interfere with your null test.

Experimenting with the null test should help you better understand phase relationships, which is a fundamental part of recording, mixing, mastering, and just about any conceivable part of audio engineering.  

So I hope this has been helpful for you – remember to subscribe to our channel, and then click the link for notifications so you stay updated on these techniques. Lastly if you have a mix that’s almost done, or one you’ve finished, and you’re curious what it would sound like professionally mastered, send it to us at SageAudio.com, we’ll send you a free mastered sample of your mix.