I know the technical explanation,i just don't understand it.
I can choose in cd dvd speed to read at 4x or at 4xCLV? Which should i choose? And what's the diff?
The speed ratings of discs always refer to the speed at which the laser is writing, not to the speed of the disc. CLV is a constant linear velocity, which means the laser writes at a steady speed and the disc slows down as the pickup head moves out toward the edge of the disc. 4X CLV means that writing speed is four times faster than the speed at which the laser would read a disc, and the laser stays at that speed throughout the disc. (In Nero CD/DVD Speed this would be represented by a straight green line for the laser and a drooping yellow line for the disc motor speed.)
4X CAV means the laser works up to a speed of 4X writing toward the end of the disc as the disc turns at a constant rate. In Nero that would be an increasing curved green line for the laser and a straight yellow line for the disc. You will find that a steady read speed of 4X CLV will be faster than working one's way up to 4X CAV, presuming that CAV is what "4X" means for your drive. (A drive spindle speed is always fastest at the beginning than at the end of a disc, that's why the claim that speeds faster than 52X will blow up discs is ridiculous: the top RPM speed of a 52X CD-R drive is little different from that of a 24X CD-R drive.)
Why don't you try it and see? It's an inexact science anyway. It will basically tell you if you if you have a good burn or a bad burn. Error correction routines in playback are going to fix a few bad PIF's.
Running at the faster CLV speed will affect the results of your quality check by probably making the score higher than it would be at a slower speed, but gjrhine is right--the disc quality does not change--only the score does, and error correction will correct errors. Nero CD/DVD Speed is a fair determination of disc quality, but it often differs from K-Probe or Plextools or DVD CATs. DVD CATs is the only truly accurate system, but it costs a quarter million dollars. That makes Nero a pretty good deal.
