An old pressed CD Audio has one single damage on the top side of the disc, which is even so bad that light can shine through it. My Optiarc burner scans brutal C2 errors from 4x to 16x. But at high speeds the C2 error is gone. At 16x the drive reports a C2 max. of 228(!) at that position. At 40x it’s only a C1 max. of 37 and a C2 max. of 0! What is the technical background of the fact, that a drive can’t correct something at a slow speed of 4x that it can correct at mad speeds of 40x and 48x?
The drive is probably optimized for high-speed reading.
I experienced similar behaviour with my old Plextor PX-712A - slowing down reading speed to below 24x when encountering errors almost always made things worse, so I disabled the slowdown setting in Exact Audio Copy for this drive.