You finally got your band into the studio to lay down some tracks. Perhaps you’re a production sound mixer, and have just finished weeks of a gruelling film shoot. Maybe you completed a field recording session of roaring race cars.

Then, when you load the tracks into your editing app, you notice a problem. Maybe there’s buzz on the guitar track. Perhaps the main character’s dialogue is soaked with hiss. You realize you set your levels too high and the stock car passes by have peaked.

It’s a frustrating experience to realize recordings captured on location are filled with problems. After all, it’s not easy to record the same audio again. Often, it’s impossible.

Not to worry. Today’s article is here to help. It shares 4 tips to reclaim and improved damaged audio.

 

Repairing Audio Problems

It’s not easy to capture completely pure audio recordings. Sound problems can occur from simple human errors, such as setting levels improperly, misaligning microphones, and more. Often environmental problems occur that damage even the most prepared sessions: noise, RF interference, rumbles, and whines.

While annoying, audio problems like these are normal. Because of this, software has been designed to fix them. Most of the time these take the shape of audio plug-ins used in tandem with editing software like Nuendo, Pro Tools, and Reaper. These plug-ins select slivers of problematic audio and fix them piece by piece.

Of course, it’s more complex than clicking a single button. Often sophisticated controls are used to tweak the settings for the finest control. Often this practice of audio restoration is a diligent, difficult, and time-consuming process with one goal: repair problems as transparently as possible.

Why is audio restoration so tricky? Well, making damaged audio sound completely immaculate isn’t easy. It’s like repairing a shattered glass; yes, you can glue the shards back together again, but the result won’t be the same as an unbroken glass. The goal is to repair audio as best as possible, however, it is nearly impossible to make a sound appear completely undamaged. Just like seeing cracks in a glued tumbler, often there are subtle problems with audio even after its repaired. So, even the best software or techniques risk creating what is known as artifacts.

With time, patience, and careful listening, damaged audio can be repaired and artifacts reduced to imperceptibility.

Let’s take a look at common audio problems and learn how to fix them:

  • Clipping.
  • Noise.
  • Rumble, bumps, and mic movement.
  • Hum, buzz, and whine.

 

Clipping

What Is It?

Clipping is a common audio problem where the top of a waveform is flattened or “clipped off”. While this smushed waveform is easy to spot, the real problem isn’t the way it looks: instead, it indicates damaged audio.

 

How Does it Happen?

Clipping usually happens when recording levels are set too high, or when sounds are excessively loud (e.g., fighter jets). When loud sounds are captured with these “hot” gain levels, recorders are overloaded, so to speak. They cannot handle the loud input. Instead, they capture what they can, and cut off what they cannot. The result? The loud sound is “clipped”, and missing part of the audio.

Why is it a Problem?

Clipped audio sounds nasty. Often it has a distorted or saturated sound to it. Beyond this unpleasant sound, clipping means that audio is not captured completely. The loudest part of the signal is lost, and not recorded at all.

How to Fix It

Thankfully, there are a few plug-ins that help. They work by looking at the audio on either side of the clipped section, and use that to recreate the damaged audio. In most cases, steps include selecting the damaged area and specifying how much the level should be reduced.

Plug-In Options

Check out iZotope RX or Accusonus’ ERA De-Clipper to repaired severed audio.

 

Noise

What Is It?

Noise is one of the biggest problems experienced when recording audio. It is an airy, hissy sound that appears throughout recordings.

 

 

How Does it Happen?

Noise is everywhere. You can hear it from fans and air conditioners. Large spaces are naturally noisy. For those recording outside, subtle wind can add a troublesome hiss to tracks. Every microphone, preamp, and recorder adds a tiny bit of noise, and low-quality gear adds more of it.

Why is it a Problem?

Just like static on a television, noise is unpleasant to hear. What’s more, noise competes with the good audio in recordings. It is broadband, meaning it can occur in every audio frequency. That means it can overlaps bass grooves, dialogue lines, and wilderness fx recordings.

How to Fix It

Noise is tricky to remove. It is interlaced with good audio. That means removing it risks taking the good with the bad.

Here are three ways to remove noise:

  1. EQ. Use equalization to roll off the high-frequency hiss. Set a low pass filter at a high frequency and gradually reduce it until you hear it robbing too much of the good audio.
  2. De-Noise Plug In. Noise reduction plug-ins work by sampling sections of pure noise (i.e., without good audio) known as a noise profile, and using that as a template for what to strip from the recording.
  3. Multi-band Compression. It’s a bit more work, but multi-band compression can often reduce noise. It’s done by soloing each band, setting the threshold for the noise level, then reducing the gain so it disappears. Discrete band controls customize how much noise is stripped from each band.

With all de-noising, it’s important to careful: removing too much strips the life from recordings at best, or adds subtle, tinkling robotic glitches at worst.

Plug-In Options

There is a broad range of noise removal plug-ins: Accusonus ERA Noise Remover, iZotope RX, Waves X-Noise, Z-Noise or Noise Suppressor, Antares SoundSoap 5, Sonnox Oxford Denoiser, and others.

One popular multi-band compressor is Waves C4.

 

Rumble, Bumps, and Mic Movement

What Is It?

Sometimes you’ll hear rumbling in recordings. It may be a constant low-end growl. It could be a momentary thump. Whichever the case, it’s clearly not part of the good audio in your recordings, and must be removed.

 

How Does it Happen?

Low-end rumble comes from a number of sources. Sometimes subtle wind or distant traffic can add low-end energy to exterior recordings. A short thump may occur from moving a microphone, or jostling it in a stand.

Why is it a Problem?

This bass rumble causes a few issues. Constant rumbling makes a sound appear “muddy”, washes a sound with low-end energy, and steals definition from the recording. Momentary bumps are distracting, and may overwhelm other frequencies of sound.

How to Fix It

This problem is easy to fix. Set a high-pass EQ filter around 100 Hz with a slope of 12 dB. Find a balance between removing the rumble and taking away too much of the good sound with it.

Momentary sounds can be fixed by using spectral repair lassoing tools to sculpt out the bump, replace it with other audio, or remove it from the rest of the frequency.

Plug-In Options

Any equalizer can be used to apply a high-pass filter to rumbling audio. Fab Filter’s Pro-Q 3 is a community favourite. You can use iZotope RX’s Spectral Repair to “pencil out” intermittent bumps.

 

Hum, Buzz, and Whine


What Is It?

Hum, buzz, and whine are exactly what you’d expect from their names: consistent gritty or nasal tones that persist through recording.

How Does it Happen?

Set up your recorder too close to an electrical panel box? Maybe your microphone is beneath a fluorescent light. Perhaps there’s a distant HVAC unit. Any of these can contribute whines, buzzes, or hums. Often they’re imperceptible, and won’t be heard until you’re in the edit suite, later.

Why is it a Problem?

Hums and whines are stubbornly intrusive. They invade not just one frequency, but multiple harmonics throughout the sound spectrum. Of course, this overlaps the good audio you want to keep, and conveys a grungy sound that must be removed from any audio.

How to Fix It

The good news about buzzes and whines is that they often occur at predictable fundamental frequencies based on the alternating current mains electricity. This will be either 50 or 60 Hz, depending on the country. So, the strongest hum will occur at that frequency (e.g., 60 Hz), and a number of frequencies above it (e.g., 120 and 180 Hz, and so on).

Target these frequencies using an EQ notch filter. That will narrow in on just that frequency without harming the ones around it. Broaden or narrow this Q to strip out the hum without affecting other sounds, and do the same for other harmonics as well.

Some plug-ins do the job more easily. They intelligently detect the hum and all harmonics of it, and slice them away in one step.

Plug-In Options

Hum removal plug-ins are available from SoundSoap 5, Absentia DX, iZotope RX, Waves, and others.

Pro-Q 3 or any other notch EQ can do the work manually. McDSP’s NF575 can find a hum frequency and automatically link 4 additional harmonics to reduce whine with a little less work.

 

You’re bound to experience these audio problems at some point during your pro audio career. Don’t worry, though, it is possible to fix them. With time, patience, and a good ear, you’ll fix troublesome audio and be back to creating albums, films, and soundscapes.