Almost everyone has run into difficult audio situations like those mentioned above at some point in their career. Luckily, there are software tools available designed to help anyone faced with the seemingly impossible problematic audio, no matter your DAW or NLE.

What is audio repair and restoration?
“Audio repair and restoration” is a phrase used to describe the various processes and techniques one can use to remove noise and other imperfections from sound recordings. 

When used correctly, these techniques can alleviate problems including:

• Ambient background noise
• Tape hiss
• Electronic interference such as hum and buzz
• Sudden background noises (coughs, footsteps, car horns, ringing cell phones, etc.)
• Clicks and pops from mouth noises or vinyl recordings
• Clipping in both the analog and digital domain

The goal of good audio repair and restoration is to render the best possible sonic result with the least audible human intrusion. Your intervention in the original recording should be transparent and not introduce new artifacts that distract the listener. Sometimes it’s possible to solve an audio problem entirely, and other times it’s about finding the right balance between reducing the problem and preserving the original audio.

It’s useful to remember that no recording is truly perfect, and any statement as such is purely subjective. Whatever your tastes, and even as times and aesthetics change, the basic intention of restoration should remain the same: render the best possible sound with the least obvious interference.

An inconsistent dialogue mix can harm the immersive experience, as the audience suddenly pays attention to issues like mismatched volume, a sudden change in sound quality, or perhaps a big jump in the noise floor.

Maintaining a consistent viewing or listening experience can be particularly difficult when the dialogue transitions between different sources, such as a studio quality voiceover juxtaposed with audio from a camera microphone on a busy street for example.

So let’s dive in:

Audio repair and restoration basics: required tools
Repairing and restoring audio typically involves working with the following types of processors:

• Denoisers are used to reduce and remove steady state background noise. “Steady state” means slowly changing noise. It might include constant ambient noise or tape hiss (referred to as “broadband” or “noisy” noise), or electrical buzz and hum (referred to as “tonal” noise because it typically exhibits recognizable pitches or harmonics). Denoisers can be single-band or multiband software or hardware, and are sometimes designed for a specific use case, such as dialogue.
• Declickers are used to reduce and remove intrusive clicks and pops. These can be caused by anything from dust and scratches on an old record, a CD skipping on playback, or even mouth clicks and lip smacks from a voiceover.
• Decracklers are closely related to Declickers, but are optimized to help reduce and remove a more continuous, quieter stream of clicks that blend together to cause what the human ear perceives as a general crackle. Using a Decrackler before using a Denoiser is often a very effective way of dealing with surface noise recorded from vinyl or shellac records.
• Declippers are used to repair digital and analog clipping artifacts. These artifacts occur when overloading an A/D converter or over-saturating magnetic tape.
• Visual Editing Tools vary by manufacturer, but the basic premise combines visual representations of audio, via a waveform or a spectrogram, with tools allowing you to select and edit certain audio events rather than the entire file.
• Dereverbs are a new, cutting edge technology, and are designed to remove or reduce reverberations from audio. They are particularly useful for dialogue editing and ADR matching, and allow the engineer to remove unwanted or distracting reverberations from dialogue recordings.

With all of these tools available, you might wonder where to begin. There isn’t a single “correct” order in which to use them—it all depends on the audio material you’re restoring. Always begin with the most obvious or obnoxious audio problem that you can hear and identify. Then, depending on the audio, it may make sense to perform some processing tasks before others.

Restoration basics

1. Back up your work. Always make a backup of the original audio file before you begin attempting to restore it. Depending on the tool, some edits become permanent once the file is saved, so it’s always advisable to maintain a prior backup. iZotope’s RX allows you to save your work and unlimited undo history as an RX document, which can prevent losing or overwriting work.
2. Keep the ears rested and the mind open. While doing audio restoration work, you’ll likely spend a lot of time focusing on subtle details. Taking breaks will help you return with a fresh mind and see and hear the bigger picture.
3. Make multiple versions. Sometimes it helps to try doing the same audio repair more than once with different settings and then compare the results. RX’s Compare Settings helps you A/B results as you go. Also, you may come back to a version you tried a few days earlier when you were tired, and now find it sounding worse than ever. This happens to all of us!
4. Keep detailed notes. This is invaluable, particularly when there are so many different methods for dealing with different audio problems. Using RX 3 document files and saving module-specific presets can save you the trouble of writing out all of the parameters on a recall sheet as you would in the analog domain.
5. Back up your work. The first and last rule of any audio editing project! You never know when a hard drive, backup device or original master might fail.

General recommendations for tackling troublesome audio
Dedicated audio repair and restoration tools can do a fantastic and fairly autonomous job, but learning when, where, and to what degree of strength to use a specific tool can yield better, faster, and more transparent results.

Additional information:
To learn more about audio repair and iZotope RX Audio Repair Suite, visit: http://downloads.izotope.com/guides/iZotope_AudioRepair.pdf