As far as Allen told me his friend put the map on top of the CD and measured on the top side with an infrared sensor until he got a minimum.
Actually the mat is black towards the disc and dark-greenish-blue on the top or was it the other way around ?
I hope i can find one and post a photograph.
I can not use it anyway beause my CD transport is a Forsell Air Reference with an air bearing.
Actually the mat is black towards the disc and dark-greenish-blue on the top or was it the other way around ?
I hope i can find one and post a photograph.
I can not use it anyway beause my CD transport is a Forsell Air Reference with an air bearing.
Chris, I'm talking about transitions that happen WITHIN a digital circuits, buffers included. It's all analog.
There is a very expensive vinyl player using laser in an analog way to read the geometrical variations of the groove.
The ELP Laser Turntable - No Contact, No Wear
Some said it sound wonderful, some said awfull. Never heard.
About CDs (or others digital optical records), nothing analog inside. Just bits. But causes of errors are many: twisted CD which can lead to outfocus the dots when the lens is not able to follow, scratches and durst which can deviate or stop the laser beam, deterioration of the fragile reflective surface, due to scratches, wear, or moisture.
There is an error correction system (EDC & ECC) to take care of those as much as possible. As far as i know, this audiophile legend of color pencil has never changed anything in the number of errors (you can monitor and count them).
And here again, there is a logical reason why it cannot work: there is no optical way a near horizontal infrared ray can be deviated to hit the lens in focus (reflection angles), and the infrared rays are attenuated rapidly by the plastic thickness: imagine the difference between the thickness of a CD and its diameter. Rays that are not immediately reflected transform themselves in low level global heat. I don't know who invent all those legends. Did Mr. Bybee sold Pencils ?
John said he never tried the pencil tip because he is lazy, I wish he had written it's because it is stupid.
The ELP Laser Turntable - No Contact, No Wear
Some said it sound wonderful, some said awfull. Never heard.
About CDs (or others digital optical records), nothing analog inside. Just bits. But causes of errors are many: twisted CD which can lead to outfocus the dots when the lens is not able to follow, scratches and durst which can deviate or stop the laser beam, deterioration of the fragile reflective surface, due to scratches, wear, or moisture.
There is an error correction system (EDC & ECC) to take care of those as much as possible. As far as i know, this audiophile legend of color pencil has never changed anything in the number of errors (you can monitor and count them).
And here again, there is a logical reason why it cannot work: there is no optical way a near horizontal infrared ray can be deviated to hit the lens in focus (reflection angles), and the infrared rays are attenuated rapidly by the plastic thickness: imagine the difference between the thickness of a CD and its diameter. Rays that are not immediately reflected transform themselves in low level global heat. I don't know who invent all those legends. Did Mr. Bybee sold Pencils ?
John said he never tried the pencil tip because he is lazy, I wish he had written it's because it is stupid.
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What does this have to do with the information content? Nothing, and that's my point. The information content is fixed in the first clocked in / clocked out buffer, barring cosmic rays and acts of Divine Intervention.
Thanks,
Chris
About CDs, they promised us they were near eternal.
I had a lot of CDs stored in a damp basement for a few years. Moisture and fungus had eaten the reflective metal layer of some of them. They were black, when i found them, and transparent once washed. No more sound out of them them. Even with the magical color pencil
I had a lot of CDs stored in a damp basement for a few years. Moisture and fungus had eaten the reflective metal layer of some of them. They were black, when i found them, and transparent once washed. No more sound out of them them. Even with the magical color pencil
My friend Don liked the sound except for the inner grooves, which became for him unlistenable. I indirectly teased him somewhere in diyaudio about the fact that he hates feedback (all the dog-chasing-tail metaphors etc.) but here was a player that used it, surely, in a very important way to keep the laser centered in the groove. Thorsten L. chided me for taking Don to task and said the servo for the position was a very slow one and should have little to no effect on the retrieval of groove information. He advised that I look at the patent.
But I'm still a tad skeptical that Don's difficulties with the inner grooves don't in some way stem from the servo --- but I'm not about to lose sleep over it. I never heard the player.
Christophe,
I don't think it took very long for most of us to realize that the marketing for the indestructible nature of a cd to be found to be nothing but that marketing. I still remember some ad where they showed a hole in a cd and the cd playing right past that! Scratches soon reared their ugly head and we had cd's that would skip just like a scratched album. I had one of my copies of Windows XP scratched by a friends bouncing read head on his cd reader make nice perfectly spaced scratches that made the disk unreadable. Microsoft would not replace it so I sent it out and for $4.50 they polished the surface of the disk and it still works today. I try and handle the cd's just as if they were a vinyl album, that way they still play after many uses. I'll remember not to store my cd's in a basement after your comment.
I don't think it took very long for most of us to realize that the marketing for the indestructible nature of a cd to be found to be nothing but that marketing. I still remember some ad where they showed a hole in a cd and the cd playing right past that! Scratches soon reared their ugly head and we had cd's that would skip just like a scratched album. I had one of my copies of Windows XP scratched by a friends bouncing read head on his cd reader make nice perfectly spaced scratches that made the disk unreadable. Microsoft would not replace it so I sent it out and for $4.50 they polished the surface of the disk and it still works today. I try and handle the cd's just as if they were a vinyl album, that way they still play after many uses. I'll remember not to store my cd's in a basement after your comment.
CDP Power Supply Interactions....
Scratched discs, out of center discs, reflections within the disc all cause increased and erratic focus/tracking servo currents.
Typical cd players run minimal quality power supplies and lousy earthing runs, hence f/t servo related disturbance of audio stage and clock power supplies resulting in degraded audio.
Looking at the analog EFM signal with a Cro tells everything about disc quality.
Dan.
Scratched discs, out of center discs, reflections within the disc all cause increased and erratic focus/tracking servo currents.
Typical cd players run minimal quality power supplies and lousy earthing runs, hence f/t servo related disturbance of audio stage and clock power supplies resulting in degraded audio.
Looking at the analog EFM signal with a Cro tells everything about disc quality.
Dan.
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I'm a great believer in car polish here: I've rescued vast numbers of CDs this way, and very cheaply. Only use the finest grade of polish, no cutter in it, and only clean radially; even very savage scratches can be eliminated with patient persistence ...
Frank
Fungus have good musical taste (Larry Carlton -Alone but never alone).
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Yes I've polished out a number of CD problems. Not much to be done when they delaminate though, although the horrible issues were with laser disks. There was a case where the industry was in denial for a long time.
I'll never forget the first CD defect that turned Emma Kirkby's voice into a repeating robot in the middle of Handel's Messiah. One expected the tractor beam from the saucer to whisk one up shortly. Perfect sound forever until it's anything but... and maybe never was to begin with.
I'll never forget the first CD defect that turned Emma Kirkby's voice into a repeating robot in the middle of Handel's Messiah. One expected the tractor beam from the saucer to whisk one up shortly. Perfect sound forever until it's anything but... and maybe never was to begin with.
fas42,
Believe me I tried to polish that data disk myself with plastic polish and the scratches were just to deep to take out that way. The company I sent the disk to actually uses a machine to polish the surface of the polycarbonate until it is again smooth. It looked like a new disk when they were done. Yes I know to polish from the center out, not around the disk as that actually can make tracks that the laser attempts to follow. It was much cheaper than the cost of a new XP disk!
Believe me I tried to polish that data disk myself with plastic polish and the scratches were just to deep to take out that way. The company I sent the disk to actually uses a machine to polish the surface of the polycarbonate until it is again smooth. It looked like a new disk when they were done. Yes I know to polish from the center out, not around the disk as that actually can make tracks that the laser attempts to follow. It was much cheaper than the cost of a new XP disk!
The polishes that the amateur telescope makers use to finish mirrors also work very well. I have a few ounces of cerium oxide that works wonders.
HA!
Though I wonder how polycarbonate would do as a record. Think it'd be a bit too brittle. SY probably has a good answer to that one.
se
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