CD Copies...why do they sound worse?


I had a theory that I haven't discarded yet that not all CD blanks are equal in terms of composition. Yes, they all are made of aluminum and polycarbonate, and when you burn a CD you are creating small holes, or dents in the blank. There is the red book standard that must be adhered to, but as in anything else, I'm sure there are better grades of aluminum and poly available, you get what you pay for. Since the laser reads the digital stream by optically scanning the surface of the CD and interpreting either a one or zero, you'd think it's a go/no-go operation. The original and copies do not sound the same, even to the uncritical ear. I thought for a while it may have had something to do with the relative quality of the CD blanks I was using to copy, in other words, the pressing plants simply use a better grade of master CD's. My friend has a contact and we were able to acquire bulk CD blanks from Saturn Disc that makes CD's. No difference, copies still aren't right. I guess we can eliminate the CD blanks for now. Here's where things get a little outside normal thinking in my twisted logic: we know there are error detection and correction schemes used in intrepreting the data on the CD, employed when the bit being read isn't immediately recognizable to the player. Is it possible the home-made copy that was burned using a cheap consumer grade burner, contains more errors? Are the pits burnt in the CD either irregular in shape or depth? Does the laser in these consumer grade CD burner introduce errors? If so, the EDAC is pretty busy, and doesn't always get it right, which would explain a general lack of quality due to latency delays in the data stream while the EDAC does it's work, and in the process is bound to mis-interpret zeros and ones, there is no 100% accurate EDAC. To me, this is a good place to start in terms of understanding the obvious differences in sound quality.
jeffloistarca
Craig, I see your point, it's well taken! They are great for the purpose you spoke of, I too use them for this. Possibly as the technology advances (which probaly won't be in the too distant future) cd recorders will be able to make exact copies. But for now I'm afraid it's not so. Take care! Hunter
Here's what's puzzling me... doesn't a CD-ROM burner have PERFECT bit-for-bit error-free capability when recording a computer data or program file? Think about it: if perfect (i.e., vanishingly small error rate) transcription and playback aren't achieved, recordable CD-ROMs wouldn't be acceptable as a reliable media for computers. Lesser performance for audio CDs and componentry is not acceptable, as low cost equipment can achieve virtual perfection relative to the writing and reading of digital data on optical media, as demonstrated by the personal computer industry.
Wow...very interesting! Could be increased "jitter" in the copies. The quality of the circuitry in the signal chain leading up to the machine used in a manufacturing enviornment certainly must be better considering the cost of the equipment and the requirement for a minimum of inconsistency in that setting. I recently had two copies of a very hi-fi CD that is out of print made, one on a PC and the other with a Phillips stand-alone copier. I haven't compared the two disks critically, but each has at least quite acceptable sound quality from what I did hear of them, although the PC made one seems to have the horn section (The music is Swing/Jazz and Western Swing, VERY well recorded, produced & mastered) a bit more "out front" compared to my recall of the original factory CD. I have to sit down and really compare these two CD copies!
Ummm... maybe you should deguass those CD's... That aluminum becomes mighty magnetized... btw... jitter is induced in the analog domain, not the digital ... (That's where CD's are copied .. in the digital domain)... In fact, CD audio is comprised of 44,000 16-bit words for each second of sample time. A CD is copied bit for bit and then verified... There is no difference between a copied CD and the original, except for in your mind and possible in your A/D converter during playback. That's the word
Too much noise, not enough jitter immunity on the digital recievers in the cd burners...this all adds up to degridation on the cd copy. Bits are not bits, don't forget the time based errors! These differences can have some of the most detrimental effects on the overall harmonic details of the copied cd. In the end, a "high end" manufacturer will eventually produce a competent sounding abeit expensive cd burner.