Tyvärr finns det ingen felkorrigering/redundans i Audio-CD standarden. Det finns inga extra bitar, checksummor etc. Missar man data vid läsningen finns det inget sätt at återskapa den annat än genom gissningar/interpolering. När det handlar om en CD för data så lagras det däremot en del extra information för att kunna korrigera felläsning. När standarden skapades tyckte man troligtvis att det var viktigare att kunna få in fler minuter musik än att den absolut måste läsas 100% felfritt.
Stämmer verkligen ovanstående? Läser man i den CD-FAQ som finns på http://www.cdrfaq.org/faq02.html så säger dom att det definitivt finns felrättning på audio cd's.
Subject: [2-17] Why don't audio CDs use error correction?
(2001/08/01)
Actually, they do. It is true that audio CDs use all 2352 bytes per block for sound samples, while CD-ROMs use only 2048 bytes per block, with most of the rest going to ECC (Error Correcting Code) data. The error correction that keeps your CDs sounding the way they're supposed to, even when scratched or dirty, is applied at a lower level. So while there isn't as much protection on an audio CD as there is on a CD-ROM, there's still enough to provide perfect or near-perfect sound quality under adverse conditions.
All of the data written to a CD uses CIRC (Cross-Interleaved Reed-Solomon Code) encoding. Every CD has two layers of error correction, called C1 and C2. C1 corrects bit errors at the lowest level, C2 applies to bytes in a frame (24 bytes per frame, 98 frames per sector). In addition, the data is interleaved and spread over a large arc. (This is why you should always clean CDs from the center out, not in a circular motion. A circular scratch causes multiple errors within a frame, while a radial scratch distributes the errors across multiple frames.)
If there are too many errors, the CD player will interpolate samples to get a reasonable value. This way you don't get nasty clicks and pops in your music, even if the CD is dirty and the errors are uncorrectable. Interpolating adjacent data bytes on a CD-ROM wouldn't work very well, so the data is returned without the interpolation. The second level of ECC and EDC (Error Detection Codes) works to make sure your CD-ROM stays readable with even more errors.
