Error correction algorithms

vbimport

#1

What is the best/most common error recovery algorithm using the ECC/EDC fields? The best I could think of is going through the sequence of interpreted bits, flipping each one, and recalculating the error correction fields and seeing if they match the one's on the disc. And if that doesn't work, flipping two bits. However, this method quickly becomes unreasonable;

Work factor of flipping all 1 bit possibilities: 18816
2 bits: 354041856
3 bits: 6661651562496
etc...

What algorithms are actually used?


#2

I’d have to look up the specific ECC used on CD-ROMS, but in general…the sector as read and the ECC as read are run through the correction algorithm. This gives one of

  • the numbers of the bits that need to be flipped, or
  • an error image that can be XORed with the sector to correct it.

It’s not a trial-and-error process.

Have you ever used PAR files on a binaries newsgroup? It works like that.

++PLS

#3

CDs (as well as DVDs) use Reed-Solomon algorithm.


#4

Originally posted by spath
CDs (as well as DVDs) use Reed-Solomon algorithm.

Yes, but how do you recover the errors using Reed-Solomon codes?

ECMA-130 gives an algorithm for creating the error correction info, but not for compensating for errors using it. (Unless I am totally blind)

I found an algorithm for correction of it in google, but it was too complex for me to understand.


#5

> Yes, but how do you recover the errors using
> Reed-Solomon codes?

You basically calculate the syndroms and solve
equations (which, in turn requires Berlekamp-
Massey, Chien,… algorithms).

> I found an algorithm for correction of it in
> google, but it was too complex for me to
> understand.

You can get good infos/code on RS on
eccpage.com. As for the complexity, I cannot
change that :slight_smile:

By the way, is it just me or this forum gets more
and more technical but not CloneCD related questions ?


#6

As for the complexity, I cannot
change that

The site you suggested made everything much clearer! Thank you! :slight_smile: :slight_smile: :slight_smile: :slight_smile: :slight_smile:

(Apparently the paper I found dealt with correcting errors via probabilities of correctness past the point where one can be certain).

By the way, is it just me or this forum gets more
and more technical but not CloneCD related questions ?

Well, there isn’t a “Leach off of spath’s knowledge while scouring the ECMA-130 forum”, so this is the next best thing. :wink:


#7

Originally posted by SirDavidGuy
Well, there isn’t a “Leach off of spath’s knowledge while scouring the ECMA-130 forum”, so this is the next best thing. :wink:

Lol!

Where can I find the ECMA-130 forum you are talking about?


#8

[OT]Ahh, yes, it could be read that way. (English is weird that way).

It could be forum “Leeching of spaths knowledge and scouring the ECMA-130”
Or "Leeching off ‘spath’s knowledge’ and the ‘ECMA-130 forum’ ".

Urgh. I’m no good at semantics[/OT]