I was given a classical recording on DAT made by a European radio
station from their master tape. Having been warned that the signal was
saturated, I recorded via analogue to ensure that I was not hit with saturation
fed through S/PDIF. In the event, it probably did not matter. I reduced the
input signal about 8 db from standard level and achieved the image seen at
left. I used Adobe Audition (formerly CoolEdit Pro) for all of the processing.
When clipping is moderate and visible only on a small portion of the signal, it is typically of the order of 3 db and correctable with Audition's Clip Restoration tool. I have found the default values quite acceptable in that case and have no formula for adjusting them for better results. The tol is on the Effects menu under Noise Reduction / Clip Restoration.
So I ran Clip Restoration on the signal with no
amplitude adjustment. The result is seen at left. Note that second-harmonic
distortion in the source resulted in asymmetry in the recovery but that overall
there was still saturation in both positive- and negative-going signal.
Here is the same signal with 12 db cut in
reducing clipping. While the positive-going signal appears to be reasonably
recovered, the even harmonics make the negative-going signal inaccurate.
However, all that was little help. Where correction of up to 3 db can be audibly 'perfect' and up to 6 db can be accepatble, restoring 20 db gave an altogether unacceptable result on even casual listening to any of the moderately loud passages; the effect on maximum levels was excruciating.