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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: Cd reading errors correction systems impact on sound. posted by beppe61 on June 14, 2015 at 07:46:18:
The TL;DR is that if you are not hearing gross audible defects it is probably not worth worrying about read errors, especially if you rip the disks and play back the resultant files.
In more detail, there are a number of things that happen to the bits on a CD if there are errors. The relative mix and impact of these scenarios depends on the type and extent of damage to the disk and the particular player used to play or rip the disk, e.g. whether or not it has a weak laser.
1. The first level of error correction successfully corrects a problem caused by a misread pit.
2. The second level of error correction successfully corrects a problem caused by several misread pits.
3. The second level of error correction detects that there was an uncorrected error and interpolates a damaged audio sample, making a small reduction of sound quality that will probably be inaudible if it is isolated.
4. The second level of error correction failed to make the proper correction, but did not realize that an error remained.
5. The second level of error correction found so many concentrated errors that it was not able to interpret the damaged portion of the disk and as a result mutes the sound for a short period.
6. There are so many errors that the player loses track of what it's doing with resulting skips and even repeats.
Problem 4 may or may not be audible, typically it is about 50% of the time and manefests as a click for each damaged sample. Problems 5 and 6 are obvious. Sometimes the problem can be avoided by cleaning or polishing a disk or using a different drive. Problems 4 and 5 may be intermittent, which is why ripping can sometimes work. I have successfully ripped badly damaged disks this way, but it can take hours and in one case this process wore out the drive that I was using.
In theory, the first two categories (successful error correction) do not degrade sound, since all the correct bits are delivered to the DAC. In practice, the processing effort involved in real time decoding of a damaged signal can degrade sound quality. The cure for this is to rip the disks, so that all the noise generated by error correction is gone by the time of playback.
My experience is that interpolation (category 3) is rare on most disks, and those disks that have these errors but no worse errors generally have only one or two isolated interpolations. The effect of the interpolation process almost always leaves only a single sample off by a fraction of what it should have been, making it inaudible even if you know exactly where it happened.
There are errors on all disks. Good quality disks generally have errors requiring only level 1 corrections throughout an entire album. There are limits on how many level 2 errors can exist on a disk before the pressing fails quality control. There are software tools that will scan a disk and tell you many errors of type 1 and type 2 were corrected and if there were any detected uncorrectable errors.
If you rip your CDs and use secure ripping software such as dBpoweramp or EAC, then you will get an error report that tells if you you got a good rip. If so, then you don't need to worry about any of these details. My experience has been that more than 95% of the time this will be the case, even though I rip a lot of questionable disks that have been poorly manufactured in the third world or mishandled (used to play frisbee with a dog?).
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- RE: Cd reading errors correction systems impact on sound. - Tony Lauck 06/14/1510:50:17 06/14/15 (1)
- RE: Cd reading errors correction systems impact on sound. - beppe61 04:06:56 06/15/15 (0)
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