hifisteve Wrote: > The thing that made me 'discover' the solution is that I was reading the > box on the Liteon DVD RW drive and saw this: > > 'SMART-X function adjusts CD-DA / VCD / DVD data extraction to a > fastest allowable speed according to both data request rate from host > and disk quality' > > So basically it's saying that it's got built in error correction for > iffy discs right? That's what made me try turning off the iTunes error > correction and 'hey presto'. > > I had been concerned that my old drive would just hammer along and > produce poor imports but no, it adjusts for bad discs too, sometimes > slowing to a fraction of normal playing speed with very bad discs. > > I've not run a test program but I have done listening tests on imports > of a very scratched discs (my wife's not mine I hasten to add) both > with and without the iTunes correction and they both seems perfect. > > It's worth pointing out that this is very impressive considering that > trying to play the discs in question on a normal CD player is a > pointless exercise, they sound awful and jump constantly. > > That said, I guess it shouldn't be a surprise, at the end of the day, > it's all just digital data and PC drives have to retrieve this stuff > accurately or programs or games would work because of corrupted files. > If a CD play has problems, the worst we hear is a dropout, click or a > jump.
All optical drives do this. I don't believe it's error correction per se. On my setup, the disc will slow down well before EAC indicates sector read errors. I assume this is some sort of low-level error creeping in, not disc read errors specifically. On mine it's pretty evident. The first track (if perfect) will rip at no more than 5-6X. This causes a "high whine" sound, indicating the disc is spinning pretty fast. Without altering the "high whine" sound at all, each successive track is faster until I get 50-60% through the disc. Then it gets interesting. When I'm pushing 10X read, some discs will cause the drive to seek around a bit. Sometimes I can hear a disc wobbling at that speed. I'll hear a loud noise from the drive, then it will slow down to a "low whine" speed, dropping to 6-7X read, gradually rising to just below the "high whine" speed as the track finishes. Often I'll hear it go into "high whine" only to drop back down to "low whine" and slow down to 6-7X again. When it resynchs on the start of a new track, it goes back into "high whine" at 10X+, which sometimes causes wobble, which will cause it to immediately drop down to "low whine" at 6-7X. This is all without EAC indicating any errors at all, which leads me to believe the drive is adjusting for other sorts of data transfer errors. CD drives are constant linear velocity (CLV) devices as opposed to old LP turntables which are constant angular velocity (CAV). In a CLV device, the data track spins by the read device at a constant speed. In a circular medium, this means that speed at the start of the disc, i.e. the centre, will be much higher than at the end of the disc, i.e. the outer edges. In order to do this on a CD player, the rotational speed decreases from 495 to 212 RPM as the read head moves away from the centre to maintain a CLV of 1.2 m/s. A CD-ROM is not limited by CLV, it can read data faster than 1.2 m/s and adjust its speed based on data integrity conditions. This jives with what I noted above, that a "high whine" (high rotational speed) only results in 5-6X at the start of the disc but 10X+ at the end of the disc. The high rotational speed at the end of the disc is so high it will cause wobbling in imperfect discs, which will cause the drive to slow down, but even though it's at a "low whine" (low rotational speed) it's still faster than at the start of the disc with a "high whine". See http://en.wikipedia.org/wiki/Constant_Linear_Velocity Episode 2 of 'Mythbusters' (http://dsc.discovery.com/fansites/mythbusters/episode/episode_10.html) shows the wobble pretty dramatically. As I said way back at the beginning of this thread, some drives are just better than others and drives are manufactured more cheaply today than they were several years ago. The data is transferred as quickly as the drive will allow. This is done on some sort of drive firmware level and the ripping program has nothing to do with the process. hifisteve, I don't mean all this to rip on you :-) but I find it interesting and wanted to see if we could determine what specifically the problem was. All we can conclude so far is that the drive itself is not correcting but -preventing- errors by adjusting its speed, and this seems to work much faster than iTunes error correction. If you were to rip the disc with EAC in burst mode (equivalent to iTunes with the error correction turned off) you'd find it much faster but you may not get accurate rips. -- Mark Lanctot ------------------------------------------------------------------------ Mark Lanctot's Profile: http://forums.slimdevices.com/member.php?userid=2071 View this thread: http://forums.slimdevices.com/showthread.php?t=22679 _______________________________________________ ripping mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/ripping
