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5. Descratcher
The Descratcher effectively removes clicks and crackles from old vinyl or shellac records, and
from audio files contaminated during recording due to switching, digital cross-talk, or thyristor
buzz.
The descratching algorithm consists of two main parts: the declicking filter and the
decrackling filter. While the declicking filter is normally used to remove heavy clicks from old
vinyl records or switching noise arising from analogue or digital audio equipment, the
decrackling filter removes any remaining, mostly small but dense clicks called crackles.
The higher the declick parameter is set, the more clicks are removed. At a setting of zero,
virtually all clicks pass through the filter. For the declicking of typically polluted vinyl records
transferred to the digital domain, a declick value of approximately 50 works well in the most
cases.
Fig.4: Typical click in the signal taken from a vinyl record (left) and restored signal (right).
The higher the decrackle parameter is set, the more crackles are removed from the original
signal. The extreme setting, close to 100, results in a smoothing of the input signal. In general,
this parameter can safely be set to 80 without any audible artefacts. In some cases, even an
extreme setting up to 100 can still improve the quality of processed audio material.
In order to minimize the occurrence of artefacts in the descratching process, the final setting
of the declick and decrackle parameters should be performed by critically listening to different
parts of the audio file to be cleaned up. We highly recommend using the difference feature of
the Playback Section, allowing optimal parameter set-up in a very intuitive way. You can
switch between the original input signal and the input/output difference, i.e., the part of
signal removed by the descratching algorithms. This difference signal normally should not
contain parts of the original signal you want to preserve. For further remarks on how to
optimally set up the decklick and decrackle parameter, see Application Tips.
Please note that the difference feature works for both Descratcher and Denoiser
simultaneously. Therefore if you want to concentrate only on Descratcher performance, leave
both Denoiser faders (threshold and reduction) at zero.
Algorithmix® Sound Laundry™ TerraTec Edition (English)
7
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