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Bit perfect rip challenge


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1 hour ago, MLXXX said:

And yet the standards for computer data disc burning provide enough redundancy that files on a CD can usually be read with perfect checksums!

Yeah but there's no redundancy at all in redbook, though you probably already know that.

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11 minutes ago, Ittaku said:

Yeah but there's no redundancy at all in redbook, though you probably already know that.

Eh?

 

Depending on how you slice it, between 25% and 75% of the data on a disc is for the purpose of redundancy.   (I'd lean towards 25%....  but 75% of the data is "not music").     It can correct quite enormous data errors, and compensate (not perfectly correct) even more Massive errors.   Optical discs just would just plain 'not work' without such.

 

https://en.wikipedia.org/wiki/Compact_Disc_Digital_Audio#Data_encoding

 

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Could there have been a beam error during exposure of the glass master, that was used to make all the CDs? Or a 'glitch' error in the software that was used to expose the glass master in real time?

 

I am surprised that the gentleman did not simply accept that there seems to be a production fault, whatever the cause, and move on. I do pity him, as you say, for his obsessive response to a problem that seems quite minor in  the scheme of things, to me.

 

There is no evidence that he has a CD player. It would be interesting to try the CDs on a player, instead of a computer drive. Just out of interest.

 

Apart from clearly damaged library loan copies, I have had incredibly little trouble playing CDs, or listening to CDs in friends' homes. In general, I would say that the error correction is very effective indeed.

 

Does anyone remember how some early CD player models had an LED on the front panel, that would flicker when an error was detected in playback? I cannot remember whether they would flicker for errors that were 100% corrected, or only for errors that were interpolated. In any case, they rarely came on, and there was never an audible consequence. AFAIK these LEDs disappered long ago.


Regards

Grant

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1 hour ago, Grant Slack said:

Could there have been a beam error during exposure of the glass master, that was used to make all the CDs? Or a 'glitch' error in the software that was used to expose the glass master in real time?

He DID say that after ripping it, the same data written anywhere always fails. There's something magical about that data. He has a sample on that page for people to download and try to burn themselves.

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3 hours ago, Ittaku said:

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The whole point of his article being that he turned off the "computer way" of reading CDs ....  ie.  read the same bit over and over until you get a reliable result (because the time taken to read each part of the disc is irrelevant) ..... and turned on the redundancy checking/correction of redbook (CIRC), which gave a better result.

 

Sorry, if I was playing captain obvious.

 

2 hours ago, Grant Slack said:

It would be interesting to try the CDs on a player, instead of a computer drive. Just out of interest.

It would v. likely work, with degraded data.

 

 

2 hours ago, Grant Slack said:

I would say that the error correction is very effective indeed.

it is.

 

CIRC corrects error bursts up to 3,500 bits in sequence (2.4 mm in length as seen on CD surface) and compensates for error bursts up to 12,000 bits (8.5 mm) that may be caused by minor scratches

 

 

2 hours ago, Grant Slack said:

Does anyone remember how some early CD player models had an LED on the front panel, that would flicker when an error was detected in playback?  I cannot remember whether they would flicker for errors that were 100% corrected, or only for errors that were interpolated.

Yes, usually just unrecoverable errors.

 

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