Understanding Click Concealment
Click concealment is the name given to the process whereby individual clicks are removed from a recording and replaced by a wave shape that is less offensive to the human ear. Because the original signal is obliterated by the click, concealment algorithms construct a replacement waveform by analysing the known waveform on either side the click.
Wave Corrector's automatic mode of click concealment is more than adequate for general use. However, audiophile users archiving treasured record collections may wish to achieve even cleaner results by utilising Wave Corrector's waveform comparison and editing functions.
These notes are provided to enable you to use these features to the full.
The Limitations of Click Concealment
All click concealment programs must balance the conflicting requirements of detecting as many clicks as possible whilst at the same time not being triggered by musical forms resembling a click. When this balance is incorrect, the result will be:
false negatives - the failure to detect a click even though it is audible to the human ear.
false positives - detecting and modifying parts of the music which the ear does not perceive as a click.
a combination of both the above.
Wave Corrector's advanced features help to overcome these limitations.
False negatives are relatively rare with Wave Corrector. However, if a click has slow rising and falling edges, then Wave Corrector may fail to identify it, particularly if the click detection threshold is set at a relatively insensitive value.
These missed clicks can usually be tracked down by using Wave Corrector's 'Block Re-scan' operation.
However, if this does not work, it is possible to manually insert one or more individual corrections. This is quite difficult because you need to learn how to visually identify a click from the shape of its waveform. Having identified it, you then insert a correction precisely over the centre of the click and adjust the width to obtain the optimum audio quality. See Inserting New Corrections for a description of this process.
False positives are rather more numerous than false negatives, but they are much easier to deal with. The vast majority can in fact be ignored since they impart only minor changes to the waveform which are usually inaudible.
However, if you wish to obtain maximum fidelity to the original recording. any corrections which do not appear to serve a purpose can be easily deleted using either the 'Block - Remove Corrections' command or else the 'Delete Correction' command if you just want to remove a single correction.
To help you identify the location of false positives, Wave Corrector provides the option of displaying a 'correction signature' in the Overview window. The signature indicates the rate at which Wave Corrector is making corrections during the course of the wave file. A high correction rate during medium to high amplitude music is probably indicative of the false operation of the click detector. Such areas should be auditioned and false corrections removed if necessary. See Removing Corrections for a description of this process.
Although the majority of Wave Corrector's auto-corrections are inaudible at normal listening levels, there are occasions when a click is not completely removed. To minimise correction artefacts, Wave Corrector retains as much of the original waveform as possible and this can sometimes allow small portions of a click to slip past the corrector. Usually, this will only affect the highest magnitude clicks highlighted in red in the correction list. (These can be located using the Find Correction commands.)
For these situations, Wave Corrector allows you to make fine adjustments to corrections. A correction can be made wider or narrower; and it can be shifted to the left or the right. By these means, the audible artefacts of the correction can be minimised. During adjustment, use the Audition commands to optimise your result.