Audio Repair 101: Clicks, Crackles, Pops
Get access to a comprehensive noise reduction guide by Emmy®-winning dialogue editor John Purcell. Learn how to control transient noises: the clicks, crackles, beeps, lip smacks, dolly squeaks and footsteps that may plague your recording.
- Noise Reduction Basics: Understand kinds of noises and how to control them
- Controlling transient noises: Clicks, crackles, pops
- Ambient Noise: Identifying and removing tonal and broadband noise
- Manually remove transient noises (and what to avoid while doing so)
- Remove transient noises using a dedicated plugin
- Control common mic boom ‘thud’
This is written from the perspective of film dialogue postproduction, but noise is noise, so what you learn can be applied to other audio recordings as well.
What are transient noises?
Transient noises range from the tiniest clicks and crackles to beeps and lip smacks to longer interruptions like dolly squeaks and footsteps. They’re everywhere in your field recordings. This article will help you locate and control them.
Transient noises can be big or small and they can occur anywhere in a track. If you’re lucky, most of them will fall between words: that makes for an easy fix. If they’re longer or more complicated or sitting no top of words, they’re harder to deal with. Transient sounds are removed with surgery rather than with EQs or other processors that affect continuous background sounds. A transient sound is an event that has a beginning and an end, so any process intended to affect the whole track likely won’t help you.
Three very short transient peaks, probably created by digital clicks. Rarely are clicks so easy to spot.
At the end of the day, there’s only one way to remove a transient noise: cut it out and fill the empty space with something that makes sense. You do it yourself or your get a processor to do it: it’s the same idea either way. Let’s first deal with noises that fall between words. For large individual clicks, it’s usually best to do this manually.
Removing transient noises between words: Manually
- Listen. figure out what what you’re going to do, and why
- Locate the noise (usually by scrubbing). Make a mark on the click so that you don’t lose it and have to search again for it.
- Cut out the problem sound.
- Find a piece of appropriate room tone and drop it into the hole. The room tone that you use should have long enough clean handles to let you create crossfades or move the edit a bit once you paste it into the hole.
- Make tiny crossfades (probably) at the beginning and end of the room tone fill. If the noise takes place in a very reflective space (i.e., with lots of reverb), it is asymmetrically longer at its end. If you’re not careful to leave a bit of the orignial reverb tail, you may create a small bump at the end of the fill. If this happens, just move the edit to the right.
- Listen. You may need to readjust the edit or find a new piece of room tone.
Here room tone replaces the noise. Make sure to get the right room tone and for the right duration.
- Listen again
Room tone
This sort of fix relies on really good room tone. Room tone is the most important tool in a dialogue editor’s bag of tricks. Think of it as the sound that’s left in a location recording if you remove all the words, body motions, and silly set noises. It’s the glue that’s used to move from shot to shot and to blast over certain noises without leaving holes. Good room tone is the Holy Grail, the perfect fishing fly.
Good room tone doesn’t always mean super quiet, super stable and clean fill sound. If, for example, in the example above, the room tone is not smooth but rather is some sort of rustly, crunchy, watery, or any other sound has an attitude, you must find a room tone that matches.
Traps to listen for when removing transients manually:
- The width is wrong:
Insufficient room tone and you’ll hear the edit.
Too much room tone and the subtle details of the fill will take on lives of their own and make the insert sound phony. - Improper room tone: You should seek room tone as close to the click as possible, so that changes in the texture of the sound don’t trip you up.
- Truncated decays: If you whacked off the tail of a natural reverb decay, you’ll hear a tiny blast of its remnants.
- Repetitive fill: If you have a string of clicks to remove, don’t use the same room tone over and over. It will sound loopy.
Removing long transient noises
Removing long events like dollies, cars, squeaky chairs, and feet almost always require replacement. You simply must find alternate takes and glue them together to produce something that matches the acting and the energy of the original. Even a long stretch of ruined room tone must be replaced with matching room tone.
Removing transient noises with a de-clicker
Removing clicks manually—at least clicks between words—is not rocket science, but when you’re up against more than a handful of clicks, or if there are lots of small clicks over words, it’s time to consider a de-clicker. A de-click plugin goes through more or less the same steps that you went through above. Let’s look at an automatic de-click plugin, in this case, Waves X-Click. All de-clickers work in more or less the same way.
X-Click plugin
Clicks have very, very short attacks, so a de-clicker knows what to look for. You define the size and shape of the clicks that you want detected. The processor then attacks only those clicks.
Before a processor can remove clicks, it must find them. X-Click defines a click based on a user-set threshold and shape. With the threshold set low, only the loudest clicks are detected. At higher threshold settings, quieter clicks are also flagged for removal. Shape sets the detection size (or length, depending on how you look at such things). Lower Shape settings detect and process short clicks; higher settings detect longer ones. It’s a balancing act between these two controls. Experiment with both of them so that you’re keeping the threshold low while still getting rid of clicks. A threshold set too high is likely to cause more damage than a shape set too wide. To understand what you’re removing—and keeping— click the “Audio/Difference” button. This lets you hear the removed clicks, and, more importantly, to know if you’re overdoing it: if you hear parts of the real signal (words, breaths feet, etc.), back off. Absolutely all de-click/de-crackle processors include this function. You just gotta have it.
The processor finds clicks based on your settings. It then deletes them and fills in the holes. In order to figure out what to use for the hole, it looks ahead, it looks behind, and it interpolates. Just like you did earlier when you replaced a click with sensible room tone. For this reason, almost all de-clickers are offline processors. It’s pretty hard to look ahead in real time! Some de-clickers work effectively in real time, but usually in one fashion or another of “reduced quality,” reserving “best quality” processing for offline work.
Traps to listen for when de-clicking:
- General over-processing: The track gets gooey, loses high-end articulation, it becomes dark.
- Loss of desired transients: With too much de-clicking, certain desired sounds may fall into a black hole. The sharp edge of footstep attacks, the sexy sound of lips parting, or particularly wet words and the like lose their edge. When you achieve just the processing you want, take a break and come back to hear if you’re turning the scene into a lifeless vanilla porridge. People do make weird noises, some of which help us connect with them, others which are just vulgar. Props can make noises that are sharp and ugly but good for mood. Think. Use your feelings to decide what to lose and what to let live.
- Added distortion: If you push a de-clicker too far, it will distort. Don’t do that.
Listen.
You can help the de-clicker do its job beautifully by manually removing the biggest of the clicks. This gives the processor better “resolution” of clicks, since it doesn’t need to deal with the small, medium, and giant clicks at the same time.
Removing mic boom “thud”
It’s pretty common to hear a very low-frequency, short-duration, not-too-loud thud on a dialogue track. This is usually caused by the boom, the shock mount, or something like that, moving about.
This kind of noise is almost entirely low frequency, so selectively using a high pass filter will probably sort it out. But if, for an entire clip, channel, etc., you get rid of everything below, say, 100 Hz, you’ll likely wreck the dialogue.
This is where you can use an offline high pass filter selectively, with an AudioSuite or equivalent process.
- Select a nice-souding EQ plugin that doesn’t have a real attitude. I use a Renaissance EQ.
- Carefully select the region around the thud; choose an area a bit wider than the noise.
- Use a high pass filter at around 90 Hz to110 Hz.
- Render.
- Move the edit around until it sounds its best. Keep the fix as short as possible.
Amazingly, you can almost always get away with this.
Traps to listen for when removing short mic thuds:
- Clicky edits. Make a short crossfade on either side of the insert. Also, try moving the boundaries of the edit. It’s amazing how a few milliseconds to the right or left can save or wreck the edit. Remember, you’re dealing with a very short insert.
- You can hear the difference between the processed insert and the surrounding clip. Shorten the insert, change the crossfade. Less insert is better than more. If nothing works, undo the process and do it again with a lower frequency on the high pass filter.
Different thuds and different tracks will require a different high pass filter setting. Make presets. Use this process when the thud sits on top of words. If the noise falls between phrases, you’re better off replacing it with room tone, like you do with any short noise.
If you still have a problem with the insert, try finding an alternate take to replace the damaged word.
What to do about crackle
Imagine a 78 rpm record. There are two kinds of surface noise. The things that you can discern individually are the clicks: chunkakka, chunkaka, chunkaka. But there’s also a steady, sandy sound that’s in the background. This is crackle. You probably won’t have to confront crackle as often as clicks, but crackle can introduce a slight edginess that usually comes with radio mics or just bad luck. (I’m not talking about the hideous mic noise that you get when the mic rubs up against cloth or hair or something else. That’s disastrous and usually requires alternate takes, wild sound, or ADR.) If you hear a non-specific edginess or sharpness that doesn’t respond well to an EQ, a de-crackler may do the trick.
X-Crackle is designed to reduce steady surface noise in old records. These may be a result of dirt or wear within the groove. In either case, the needle moves more randomly than it should, which means low-level meaningless noise.
Although you won’t find this specific problem in film dialogue, you can use this plugin to take the edge off of certain tracks.
There’s a very slight chance that a de-crackler can mitigate the horrors of distortion if you make repeated passes with the processor, beginning with an agressive pass, and then move to a series of light passes. Select the smallest area possible. It may help with the distortion, but likely at a cost.
Traps to listen for when de-crackling:
- The track becomes dark and muddy: Transients add sparkle to a track, so if you iron out too many of the sharp edges, the track gets dark. If used judicioiusly, though, a de-crackler can make the track a bit more elegant.
- Distortion: Over-process and you’ve removed too much of the original sound. Too much synthesis can lead to chunky distortion and maybe even clicks.
The next article is about understanding and then controlling ambient noise; the rumbles, roars, hisses, and whines that cover scenes and separate us from the story.
Read the next article in this series: Ambient Noise: Identifying and removing tonal and broadband noise »
Emmy® winning sound editor John Purcell is the author of Dialogue Editing for Motion Pictures: A Guide to the Invisible Art. He writes for Waves Audio.