Dialogue Editing

Fixing Noises 201
Repairing Distortion with De-Crackling
Distortion can’t be removed. Really, it can’t, and your only recourse is to
replace the distorted words with alternate material. However, when your
back is against the wall and there’s no choice, de-click and de-crackle may
help. Why? Look closely at the waveform of a distorted track and you’ll see
two main problems. First, the waveform is truncated, like sawed-off pyramids.
That gives you the ugly compression of a distorted sound. Second, the
plateaus are jagged and rough, not unlike the waveform of a 78-rpm record.
As with removing clothing rustle, repeated passes of a de-click utility followed
by de-crackling may smooth the rough edges and even rebuild some
of the waveform’s natural contours.
Make a copy of the section of the waveform you’re repairing to get
back to the original soundfi le if necessary. Processes like de-click and
de-crackle often add a bit of level to a region, so make sure that there’s
at least 3 dB of headroom in the original soundfi le when you start this
operation. 2 It’s not good enough to lower the level through volume
automation. You have to lower the level of the original fi le before
making the copy. Or you can make a copy with the “Gain” AudioSuite
processor, which will result in a new soundfi le with enough headroom
to accommodate the peaks that will likely result from the de-click and
de-crackle processes.
Start with the de-clicker on a very high threshold setting. One of the
few good things to say for distortion is that most of the damage is
confi ned to the loudest material. That’s why you start with a very high
threshold, leaving the undamaged majority of the signal unaffected. In
essence, what you’re doing is aggressive processing on the topmost
part of the waveform.
After one very powerful pass, apply fi ve or six additional passes, each
one less aggressive than its predecessor. Remember to keep the
threshold high to avoid harming the undamaged, lower-level material.
Repeat the same process with the de-crackler. Begin very aggressively
and then progressively back off.
Many restoration tools allow you to monitor the removed noises, switching
between the dregs you’re removing and the cleaned results. This is handy for
determining if you’re overprocessing. If you can hear components of the
2 If you’re working with 24-bit soundfi les, you can afford to drop your level by 6 dB
since you have such a huge dynamic range available.