CD Error Correction Circuitry

[pauljones]

Hopefully someone can help me with this question: I have owned many CD players and recorders, and all seem to play damaged (badly scratched) CD's with varying degrees of success. While I handle CD's with the utmost care, I have purchased and/or have been given some in very bad shape. Out of all the high end players and others I have owned, one outshines the others by far as its ability to play damaged discs. It is a portable Panasonic purchased in 1997, model SL S120. Not only is the player very musical and crisp without sounding brittle, it will play virtually anything, no matter how badly damaged, without any audible artifacts. I am wondering why this little gem of a player will outperform many other players costing many times more!

[Grant]

Paul, I have the Panasonic portable SL-S261C, and it is very robust as well. I haven't really compared the sound to any other player, though.

[Paul Chang]

Error correction is used as a broader term here. Besides the Cross Interleaved Reed-Solomon Code error correction system, the transport's servo system also play a major and bigger role.

Even though they were all designed following the Philps/Sony "Red Book", the Reed-Solomon Code decoders in your different CD players may utilize different algorithms, which all consist of essentially the same sets of procedures, depending on who made the controller ICs. In the other words, different flows of the same actions.

I don't believe the error correcting capability makes as significant a difference as the tracking capability of a CD transport in digital audio play back. One obvious reason is that different R-S decoding algorthims, however distinct in themselves, are very similar anyway. It's like giving different cooks the same kitchen equipments and asking them to make the same dish following the same recipe.

Then what makes the same dish tastes so much different. It is in the ingredients, the raw materials! One cook may get fresh food but another be given rotten stuff with some spices missing.

But you were playing the same disc, the same plateful of bits. :confused: So something happen on the way to the kitchen. Believe it or not, your Panasonic portable may have the most robust laser pick-up/motor/servo system amongst your gears. I found chasis CD players to have poor to none anti-shock capability. They are not meant to be strapped on a jogger's waist. :D Nowadays most portable players have anti-skipping buffer memory, which translate to bigger elastic buffer in the ratational servo and that can help too.

My theory (to be refuted/disproved :) ):
Damged discs and vibrations have the same effect on the CD transport - making the spinning disc more difficult to track. When the player had problem tracking, either caused by bumpings or scratches on the disc, the bits in the buffer get depleted. In a portable, the larger buffer not only work in tandem with the shock absorption to make it more immune to vibrations, it helps alleviate the difficulty in tracking a bad disc, too.

Paul J.,

If your SL-S120 has anti-skipping, turn it off to see if it makes any difference. However, its base elastic buffer could be larger than a chasis player's to begin with.

[pauljones]

To Paul Chang, thank you very much for your reply! What I am sure you will find interesting is that my Panasonic portable has no buffering or anti-shock capabilities whatsoever! I had used it in my bedroom with the system I employed there (Pioneer 200 watt stereo receiver, Zenith stereo tv, etc. but now listen to it every day as part of my critical listening system. Thanks, Paul.

[Paul Chang]

Paul J.,

That means your SL-S120 has only the elastic buffer in the ratational servo. The ratational servo controls the speed of the motor such that the buffer is about half full at all times. It could still be larger than that in a chasis CD player. I don't think its size is specified as one size fits all but I don't have a "Red Book" to confirm it.

There can be other factors in the tracking capability, such as one-beam vs. three-beam focussing. No matter what the reasons are, it is quite revealing that a portable CD player can outperform more expensive chasis models.