jay@allegra.UUCP (Jay Hyman) (07/15/85)
The February, 1985 issue of Communications Magazine (IEEE) had a cover story on the communications aspects of the CD player which I have found very helpful. (Now I know what "oversampling" means in this context, etc.) The piece was written by Hans Peek from Philips, and describes the CIRC error coding scheme in detail. While it seems to be pretty robust, he suggests two possible improvements to the error correction systems: "multiple-level reliability information (that is, distinction in flag qualities such as certainly in error, and less probable (sic) in error)... may be provided in future generations of CD players." And in interpolating missing samples, while linear interpolation is described as the current technique, "restoration is always possible by using adaptive interpolation... Although adaptive interpolating is not used in current players, it is a future possiblility." In the D/A section, he describes the use of 4x oversampling with 14-bit converters (he doesn't specify one or two.) My question is this: given that the differences between CD players are said to be in their error-correcting capabilities, what do the more expensive ones do? Are there CD players on the market now that already use these "next generation" techniques, or do they do other things differently (and what) ? Do any players use straight 16-bit converters with analog filters? More generally, do the things explained here characterize all CD players on the market, or just one particular Philips model? And one less technical question: the Philips player pictured on the cover looks exactly like the Magnavox model 1040 a friend of mine just got for about $200. Are they identical, or just packaged in the same housing? Jay Hyman allegra!jay
karn@petrus.UUCP (Phil R. Karn) (07/15/85)
My "gut feeling" is that any further improvement in the error correction mechanisms is likely to be well beyond the point of diminishing returns. On the other hand, efforts to improve the laser tracking servos would be very worthwhile. The only time I've heard audible clicks or mutes from my CD player is when the servo jumps a track, either due to a defect on the disc or physical vibration. No improvement in the error corrector can handle this. Phil