puzzlement on DVD drive continues

[arethinn]

Last night I burned a DVD and as far as I can tell the data is all fine. I'm not going to sit here and play every single mp3, but all the directories and files seem to be there and the ones I have played do play just fine, without any of the audio garbling. So it seems to be only audio data being played from whatever disc is in the drive. I am so totally confused.

I suppose since I have a perfectly good standalone DVD player in my room and would therefore not be intending to play DVDs on my computer anyway (except maybe for screen captures) that this is more annoyance than showstopper, but it still bugs me that it doesn't work right.

Comments

[twopiearr.livejournal.com]

obligatory dumb question: you maxed out on good, fast RAM? anecdotal evidence suggests that's the most likely culprit in otherwise totally inexplciable multimedia glitches.

[starlightforest.livejournal.com]

1GB of RAM. It's only PC133 and not DDR because that's all the computer is (PIII 1.2), but I see no reason it shouldn't be sufficient. Besides, as mentioned, video transfer is fine, and I would think that would be the first place to take a performance hit if there were problems.?

The nature of the corruption.

[foxgrrl]

The data you read [For CDRs burned on another drive] will look ok. But it's not. All of the files and directories will be there -- that's only a few sectors of disc space, statistically unlikely to be bad. But a random 2048 byte block in the middle of a file somewhere will be complete garbage. And you won't know until you go to use that, since the drive never reported a read error.

What I do, and you should do too, is calculate MD5 hashes for all of the files I burn onto a disc, and then after I burn a disc; I read the data back off, recomputing and checking the hashes. You can also use CRC32, or SHA1, or your favorite checksum functions, if you like.

I think that most of the times when I burned a DVDR in that drive, and immediately re-read all the data back, everything was fine. But I still don't trust it for long-term storage.

(There was another drive the last place I worked, that burned DVD+R's that self-destructed after about 5 days. Burn goes fine, reading all the data back is fine. Put it in a case, in a dark box, on a shelf. And a week or two later it's full of hard sector errors, if anything is even readable at all. I thought that it was a bad batch of media at first, but after going through three spools of DVD+R and DVD-R's manufactured in different pressing plants; It had to be the drive. (And not one individual drive, it was every drive in the office of this brand. (I think SONY.. something, I can look it up in my notes.)))

More technical details about CDs

[foxgrrl]

I forgot to mention before. Compact Disc Digital Audio (CDDA) "Red Book" uses less error correction than data (Mode1) "Green Book" CDs. So it's much less tolerant of errors. DVDs also use less error correction than data CDs as well. And they squish the tracks much closer together on DVDs, and various other physical characteristics have lower tolerences than CDs.

(I'm going to skip the whole discussion about Reed-Solomon codes, and C1 and C2 errors, and the minute details about how the lands and pits read by the laser get turned back into data. (Since I don't think anyone will care.))

Anyway, in summary: Audio CDs only have two layers of error-correction, Data CDs have three layers. So marginal errors that make it past the first two error-correction passes, but are caught by the third, will not effect Data, but will effect Audio.

By the way... when you say the audio is "garbled", in what way specifically? Different types of error conditions garble audio differently. And I can tell a lot of different problems apart by ear.

Is it:
1. A short, high frequency 'click'?
2. A short fragment of sound from a different part of the song?
3. A short burst of white noise?
4. St-St-Stuttering?

Re: More technical details about CDs

[starlightforest.livejournal.com]

Sort of like a combination between a skip and a pop. I will see if I can record a sample of it at home.

Re: More technical details about CDs

[starlightforest.livejournal.com]

Sample of the sound problem (http://eristic.net/sample.mp3)

Ignore the high-pitched staticky clicking. That just showed up when I started recording and isn't in the actual playback. Listen for the fap-fap-fap, slowed-down helicoptor rotor noise.