Repairing A Clipped Signal
Complex hard-clipped signals (recorded at CD resolution or less) cannot be restored to their original state because the information contained in the peaks that are clipped is completely eliminated. Soft-clipped signals can be restored to their original state to within a case-dependent tolerance because no part of the original signal is completely eliminated. In this case, the degree of information loss is proportional to the degree of compression caused by the clipping. Lightly clipped bandwidth-limited signals that are highly oversampled have a high likelihood of perfect repair.
It is preferable to avoid clipping, but if a recording has clipped, and cannot be re-recorded, repair is an option. The goal of repair is to make up a plausible replacement for the clipped part of the signal.
Several methods can partially restore a clipped signal. Once the clipped portion is known, one can attempt partial recovery. One such method is interpolation or extrapolation of known samples. While this is only an approximation of the original, the subjective quality is usually improved, sometimes with no audible difference.
Other methods may also be used. One of the methods in CuteStudio Declip, for example, works by copying the signal directly from one stereo channel to another, as it may be the case that only one channel is clipped.
Several software solutions of varying results and methods exist to counteract this problem: Sony Sound Forge, iZotope Rx2, Adobe Audition, Nero Wave Editor, and a plugin in the Audacity LADSPA package come with clip restoration software. There is also an Audacity plugin called Clip Fix that uses cubic splines to attempt to restore a continuously differentiable signal.
Read more about this topic: Clipping (audio)
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