Why CD players will never be dead

" "Error correction," which as I understand it occurs many times during the reading of a typical cd, is by definition bit perfect, i.e., the error is corrected!”

Hi Al, please take this as a question and not an argument: If information (bits) is missing from a read, how does a CDP know what that information is. It was my understanding that error correction/interpolation/concealment is a process where the CDP makes a sort of guess based on the before and after the error bits. Okay Steve, blast away :-)

11-28-11: Phaelon
If information (bits) is missing from a read, how does a CDP know what that information is. It was my understanding that error correction/interpolation/concealment is a process where the CDP makes a sort of guess based on the before and after the error bits.

Hi Tom,

Good question. The answer is that what are called "error correcting code" bits are encoded onto the CD, in addition to the audio data (and other) bits. As explained in the first Wikipedia writeup I linked to, those bits implement mathematical algorithms which allow errors in the associated data bits to be detected, and if the errors are not extremely severe (as may result, for instance, from a particularly severe scratch on the CD), also allow the exact original data to be determined.

That process is performed by the transport mechanism's electronics.

In the far more rare event that the errors are too severe to be precisely corrected, then interpolation (aka concealment) is performed, which as you realize amounts to an estimate or guess as to what the data should be. Or in extreme cases the CDP may mute, or if a non-realtime read mechanism such as a computer or the Perfect Wave transport is being used, multiple attempts may be made to read the incorrect data.

Note this sentence in the Wikipedia writeup:

The result is a CIRC [Cross-Interleaved Reed-Solomon Code] that can completely correct error bursts up to 4000 bits, or about 2.5 mm on the disc surface. This code is so strong that most CD playback errors are almost certainly caused by tracking errors that cause the laser to jump track, not by uncorrectable error bursts.

Best regards,
-- Al

Thanks Al. Terrific explanation.

So according to that wiki and what I previously thought, it is A COMPLETE FALLACY that the audio cd player reads a different set of data each time and products like the ps audio perfect wave are relying on pure marketing to make people think cd reads are inaccurate.

No.
An uncorrectable error burst is just one of many issues addressed elsewhere in this thread.
Your 'complete fallacy' assertion would take quite a major leap of faith to believe.
On paper, in a perfect world, there is no reason for a CDP not to read a CD exactly the same way, every time. We don't live in a perfect world. Something else is at work here.