Dennis Gunn... > I could be wrong but think there is some kind of error > correction redundancy in computer type data files (i.e. > SDII or AIFF files) that is left out when they are > converted into the format that is used on audio CDs. The error correction doesn't happen at the file level, it happens at a lower level. SDII, AIFF, WAV files, are all quite similar: long long lists of sample values, in order of playback. When this string of samples gets stored on some magnetic media, that's when the data gets written redundantly. There is also error detection and correction that happens in the communication between the CPU and the storage device. The CPU checks to see if the incoming data is OK, and if it isn't, it asks the storage device "what was that again?" and the storage device resends the data. Same with modems. > I guess CD players have some other method of detecting and > compensating for errors. CIRC, or Cross Interleaved Reed-Solomon Code, is one of many error detection and correction algorithms. The math on these subjects is intense; I've tried to study it, but it bounced right off me, so I can't go into detail about how detection and correction works beyond the simple stuff like parity. > Anyway as I understand it that is why you can put more > songs on an audio format CD than you can if you are burning > it as a data format CD. The error correction is more robust on data CDs - but this takes place at the sector level, rather than the file level. CD rom sectors have greater redundancy than CDDA sectors, therefore the amount of data that can be stored in them is smaller, but it's less likely to go corrupt. When Sony was developing the data format portion of the CDDA standard (in conjunction with Phillips, who handled the optical pickup side of things), they took into account the fact that audio playback can withstand a few dropped bits by compensating with interpolation. They assumed that samples would be interpolated fairly regularly, and took advantage of the relatively high resistance of PCM audio data to audible problems therein and decided to squeeze even more audio into an even smaller space. A dropped bit in a computer file is a much more serious problem - think of the chaos that would ensue if a dropped bit in your accounting file caused a positive number to become negative! Marvin Humphrey ............... marvin@... ----- Sent using MailStart.com ( http://MailStart.Com/welcome.html ) The FREE way to access your mailbox via any web browser, anywhere!