10 common uses for audio restoration in mastering

iZotope RX is used for audio repair and restoration in many different industries: film post production for dialogue editing, audio archival to preserve important recordings, law enforcement for forensic purposes, to name a few. The repair tools in iZotope RX are also helpful in the mastering process to remove unwanted mouth clicks, room sound, or distortion to help a musical work reach its fullest potential. 

A key difference between using audio repair in a musical context versus a more a straight dialogue-centric context is being aware that “corrections” may ultimately be a part of the aesthetic of the music. For example, certain kinds of distortion might be intentional – the tape hiss you hear in the quiet sections of music may be wanted, and blanket cleaning up of plosives across a stereo track may weaken any low end transients. 

Like most things in audio, nuance and context is crucial. In this article, we’ll cover a few of the most common uses of audio repair in mastering. We’ll also talk about discernment and artistic integrity: two very important parts of the creative process, including when you are fixing audio. 

If you’re hoping to learn more specifics about the differences between types of background noise, ticks, pops, etc – check out this article.

Follow along with this tutorial using iZotope RX.

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So what do we really mean when we talk about audio “cleanup” in general? Perhaps more than any other topic in audio, this particular subject spans all media – movies, television, podcasts, music. It can mean fixing bad ticks and audio pops, removing background noise, matching ambiance, improving intelligibility – as well as rebalancing musical content in a pinch or removing excess reverb from a recording. Sometimes the music is recently created, other times it might be a digital transfer from a tape from many years ago. In that instance, audio restoration can be helpful in the remastering process.

1. Removing Clicks and Pops

Perhaps the most “ordinary” cleanup of audio, whether music or straight dialogue, is removing clicks and pops. These sorts of sounds can be introduced throughout the recording process; a dropout during a recording, a bad edit during a mix, a mechanical noise in the tape transfer process. In these instances, once the nature of the sound is discerned, De-click is extremely helpful.

2. Spectral Repair

The spectrogram in RX affords us the benefit of visually placing noises in a specific frequency range and time within an audio file. The bolder the color, the louder the offending sound is in the mix. Through the different selection tools, we can hone in on one frequency. Instant process allows for instant fixing right as you select the audio. I don’t always find this as useful when I’m tweaking a specific glitch I’m trying to clean out; if it doesn’t work, then I have to keep undo-ing. I’d rather use the compare function in the module and find the right settings that way.

Spectral repair is incredibly useful for all sorts of problems. Ticks and pops, “analog” sounds – like a chair squeak or a bumped mic, to fix a plosive that is hard to get out – hopefully by the time you get the files for mastering, these will all be addressed. But as we know, in mastering, everything usually becomes more apparent, good and bad! So you might hear things that were missed in the mixing process. 

That being said, sometimes page turns, mechanical sounds, amp sounds add to the context of the mix, and if removed would make things sound unnatural. I once recorded a solo piano recital where the pianist would sometimes hum or sigh, kind of like how Glenn Gould hummed when he played piano. I didn’t want to remove the sounds entirely, as they added to the performance and it would have been difficult to do that and have it sound natural anyway.

3. Dealing with problems in the left or right channel

One of the most versatile things in RX is to be able to choose to affect the Left or Right channels separately. If you select L or R in the editor window, you’ll see the unselected channel go dark, which means you won’t be affecting the audio.

Removing a click using De-click, Spectral Repair

In this example, we have a click in a stereo mix that is most likely from a bad edit. We can use both De-click, the left and right selection tool, and Spectral Repair to take care of it.