Getting rid of digital "zippers" with Sonic Solutions
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(Questions or comments? Talk about it on the logblog.)
In this example, we deal with a brief burst of noise (often referred to as a "digital zipper") at approximately 12:47 in the 4/17/72 Dark Star.
You're looking at four screen shots of an edit list in the Sonic Solutions digital audio workstation. In each of these images, the upper trace is the left channel and the lower trace is the right. The "zipper" affects only the left channel, so we have a convenient visual comparison for each step of this operation.
Most of the noise bursts of this type show up as two distinct collections of digital spikes. (There are other forms of digital noise that are variously easier and harder to identify and remove, but the "zipper" is a common occurrence in DAT transfers. This may have something to do with what I have heard some engineers refer to as "head clogs" on DAT machines.)
Sonic's declicking algorithms work by analyzing the surrounding audio and interpolating a highly-educated guess as to what should go where the diginoise is. There are six options in the NoNoise™ menu, arranged in descending order of utility. The most-often-used algorithm, "B-type" (they were named in order of their creation at Sonic Solutions), has two additional options: L->R, which is used when you want to take most of your contextual information from the left (earlier) of the trace, and L<-R, which analyzes based on the sound that follows the target area. This is useful in situations where you have, for example, a large drum hit right after the affected area. I've found that it's best to deal with zippers by processing the two bursts separately.
In the upper left image, I have placed the "gates" around the second burst of noise. For no particular reason, I am doing the right half first.
In the upper right image, you can see the result of my using the "B-type, L<-R" menu item to eliminate the second half of the zipper.
In the lower left image, the gates are around the first half of the zipper. I actually placed the gates much closer to the diginoise before executing the command.
And in the lower right image, you see that the noise has been completely eliminated and the upper trace looks very much like the lower trace. There is a red bar above the waveform wheverer NoNoise™ has been applied.
Click here to hear the "before" and "after" audio.
And here are two examples of the subtler, harder-to-spot zippers:
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