Audio repair and restoration: tools of the trade

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Audio repair and restoration tools can do a fantastic job, and learning when and how to use each tool will yield better, more transparent results

Audio repair and restoration with RX 4

This post on audio repair and restoration is excerpted and adapted from Audio Repair And Enhancement, a guide produced by our friends at iZotope. Reprinted with permission.

In today’s world, audio and video recordings can be made by almost anyone. From smartphones to sophisticated studios and sound stages, large amounts of media content are created daily. As our world becomes increasingly and audibly congested, the rate of ruined recordings is rising in tandem. Human error, unexpected electrical or mechanical interference, and unwelcome intrusions from aircraft, cell phones, pets, people, and Mother Nature regularly impact even the most seasoned professional. Many times, it just isn’t possible to record that “perfect take” over again, particularly when editing coverage of a live event, or working to meet budgets and deadlines.

When you hear the words “repair” and “restoration,” you might be inclined to think of dusty vaults filled with aging master tapes and records. Some audio repair and restoration projects may indeed involve taking old recordings and reviving them, and the same methods and tools used for those projects can be used for a wide range of scenarios. Every time you record audio – whether at home, in the studio, or on location – there’s always the chance of encountering unexpected and unwelcome audio “guests.”

“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 such as:

  • Ambient background noise
  • Tape hiss
  • Electronic interference, including hum and buzz
  • Sudden background noises (coughs, ringing cell phones)
  • Clicks and pops from older vinyl, shellac, or phonograph 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. In essence, 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. The basic intention of restoration should remain the same: render the best possible sound with the least obvious interference.

Audio repair and restoration tools

Repairing and restoring audio typically involves working with the following types of processors.

Denoisers

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 “broad-band” or “noisy” noise), or electrical buzz and hum (referred to as “tonal” noise because it typically exhibits recognizable pitches or harmonics). Denoisers can be spectral or multiband, software or hardware (such as iZotope ANR-B), and are sometimes designed for a specific use case, such as vocals.

Declickers

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

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. (Tip: 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

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

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

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.

General recommendations

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.

For example, a loud hum, a heavy crackle, or severe clipping might at first prevent you from hearing and dealing with additional audio problems. Peeling away that first layer may make the next step more obvious to you. Don’t be afraid to try out different combinations of the tools to get the result you want.

We highly recommend that you educate yourself about the function of individual tools in your toolbox. 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.

It’s also beneficial to establish your aim before setting out. Do you want to treat each file with individual care and attention, or would you rather define the most appropriate settings with which to batch process hundreds of files quickly?

Quick tips

  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.
  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.
  4. Keep detailed notes. This is invaluable, particularly when there are so many different methods for dealing with different audio problems. For forensics work, documentation is often a required deliverable.
  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.

This post was excerpted from iZotope’s guide to Audio Repair and Restoration. Click here to get a PDF copy of this and other free guides from iZotope.

iZotope makes innovative products that inspire and enable people to be creative. Based in Cambridge, Massachusetts, iZotope has spent over a decade developing award-winning products and audio technologies for professionals and hobbyists alike. Used by millions of people in over 50 countries, iZotope products are a core component of GRAMMY-winning music studios, Oscar and Emmy-winning film and TV post production studios, and prominent radio studios, as well as basement and bedroom studios across the globe. Through a robust licensing program, iZotope also powers products made by industry partners such as Adobe, Avid, Microsoft, and Sony. iZotope was recently honored with an Emmy® Award for Outstanding Achievement in Engineering Development for its flagship audio repair suite, RX®.

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