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SHM-CD Format: Hype or Hope?, Metallica's New Album
knutinh
post Nov 11 2013, 21:34
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QUOTE (greynol @ Nov 11 2013, 17:41) *
Rather than more hit-and-run posting

Please state what post you are referring to.

-k

This post has been edited by knutinh: Nov 11 2013, 21:44
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pdq
post Nov 11 2013, 21:43
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QUOTE (knutinh @ Nov 11 2013, 15:34) *
QUOTE (greynol @ Nov 11 2013, 17:41) *
Rather than more hit-and-run posting

Are you referencing my post?

-k

I'm sure he was referencing rod's post.
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extrabigmehdi
post Nov 12 2013, 01:37
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QUOTE (krabapple @ Nov 11 2013, 20:07) *
Bob Katz has an unfortunate habit of citing 'blind tests' whose salient details he's never published.


Thanks for the remark , I took a quick look to the mentioned paper, and I was a bit disturbed when Bob Katz talked of blind test.
And it seems he's a famous/popular audio mastering engineer , so it would tempting to take his writings more seriously.

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Glenn Gundlach
post Nov 12 2013, 07:12
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QUOTE (knutinh @ Nov 11 2013, 05:41) *
The CD is still a physical format, and there must be some control mechanism wrgt how fast the CD spins, some local clock oscillator, the physical signal on CD and the digital/analog signal pushed out of the CD player. This control mechanism might be implemented with variable degrees of decoupling, stabilisation, delay, cost etc in mind. Intuitively, it sounds like an engineering problem that can be "solved", this does not mean that all solvable engineering problems are solved in practice...

<snip>

-k

The job of the servos (plural) is to keep the disc speed correct and the laser beams (plural) properly focused and on track. The LENGTH of the pit is the EFM binary value that gets looked up to convert back to plain binary. The data is not recorded sequentially in order to cover burst errors. Disc damage will come in spurts of 'N' bytes long and it's difficult to fill in big holes so the data is 'scrambled' by writing into RAM line by line and reading it out column by column. The reverse is done during playback. So, instead of having one big 'N' byte long hole you end up with 'N' 1 byte holes. Error detection and correction data is added during record. Small numbers of errors can be 100% corrected and bigger errors get interpolated which is obviously not good but the disc has to be pretty messed up to get to interpolation.

More error correction is added for data mode when used for files. Programs can tolerate no errors and still work correctly so the basic medium has to be pretty robust.

Timing errors off the disc show up as a variable write speed into the descrambling RAM and when read out with the stable clock all your jitter is gone. It's called Time Base Correction and has been done in video for over 50 years so it was nothing new for CDs, just an even better implementation than in early video TBCs

Bottom line is if the disc could not be bit perfect, it would never be useful for software.

Some players ARE more tolerant of poor discs - better servos and analog signal processing. Remember, there is no such thing as a digital recorder. The digital signal controls an analog signal that gets recorded, transmitted or transfered so anything that distorts the analog signal potentially degrades the digital signal encoded into the analog stream. Don't believe me? Get a scope and look at digital transmissions and recordings. BTW it's what I do for a living in broadcast TV.

G
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