Removing Phone Interference from Audio

Recently when editing our last 24hr film ‘The Last Day’, I was annoyed to find the audio track was plagued with mobile phone interference in certain places. I thought nothing could really be done to fix it but after speaking to a few people via Twitter I heard that the audio could be fixed with noise reduction and click removal. I tried in Adobe Audition to no avail until I read about iZotope RXII, an advanced audio repair tool. I decided to give it a go and it is brilliant, a fantastic audio tool well worth it’s price.

The problem with phone interference is that it invades your audio track at all frequencies. Check out the example below. The lines of squares are the phone interference, you can see they are evident all the way through the frequencies.

For certain types of interference the click removal tool works wonders but it doesn’t work with long buzzing type interference, only the clicking/popping type most people are familiar with. The example we will be looking at here is the final scene of ‘The Last Day’. The countdown to midnight (the end of the world?) is unfortunately plagued with interference and really distracts from the scene. Listen to the example below from the original footage.

Here is the audio from this clip loaded into iZotope RXII.

You can see the lines of squares plaguing the audio throughout. Luckily there is interference at the start of the clip before any dialogue. This is where we can take a noise example from. You simply select the noise you want to remove and click ‘train de-noiser’. We now have a example of both the interference and the ambient sound in the background. Once we apply the noise reduction to the audio it will have removed both interference and background audio, so we will need to add some ambient sound back in later. Here is what the audio looks like after it has been treated.

We can now export that and add it in along with some mild wind noise in the background. Here is what the audio sounds like after the repair.

The difference is massive and the dialogue hasn’t become overly tinny like some other software produces. This method only works if the scene contains background noise that is quite loud or possibly some music. The repaired audio isn’t perfect and will need something to cover it up.

This quick method won’t give the best results possible but it’s easy to accomplish and can give audio good enough for web delivery and can certainly save the day if needed. Moral of the story is make sure everyone on set turns their phones off!