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Post by Barrington on Apr 6, 2016 12:55:28 GMT
What and why and are they any good ? Ta  |
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Post by dsjr on Apr 6, 2016 13:21:27 GMT
I have no real idea, except to say that commercial discs are/were made of soft scratchable plastics to the lowest common denominator, at one time with errors way outside the Red Book spec and with some makes bronzing badly* in the late 80's to early 90's causing severe read errors. Maybe the gold ones last longer and are in any case better made?
*I liked the raw but honest Dove Records CD issues of the first three Ozric Tentacles albums, as the sound was lively, clear and full of energy. These discs suffer from bronzing and reading issues after a few years. The later mid 90's remastered albums didn't seem as good. inverted phase was one issue, but I don't know if some slight compression wasn't added too? Not sure about current CD pressings though. I have couple of other discs, one a Level 42 disc from the mid 80's which isn't as shiny-silver looking as it was when bought. I'll have to play it to see if it's damaged..
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Post by MartinT on Apr 6, 2016 16:26:22 GMT
There are gold coloured CDs and real gold CDs, difficult to tell apart. The Mobile Fidelity Ultradiscs really do sound good.
I had a few CD-Vs that suffered from the famous laser rot, most of which were replaced by Polygram Blackburn. The bad discs all came from them, as I remember.
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Post by Barrington on Apr 6, 2016 16:34:13 GMT
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Post by daytona600 on Apr 7, 2016 8:35:59 GMT
24K CD all phased out years ago & replaced with hybrid sacds from the Audiophile labels
some are now worth a few bob
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Post by zippy on Apr 7, 2016 10:00:02 GMT
The subject was much discussed a few years back as regards the use of CD's for computer data storage, and whether the discs degraded over time, and whether gold discs were better than silver.
It is still possible to buy 'archival grade' gold data CD's which are said to last for 100 years. Strangely I can't find much data relating to commercially recorded CD - I've even seen a figure of 20 years quoted but I find that ridiculous as I have loads of CD's that old and showing no sign of degradation.
(I also remember discussions about whether you should paint the back surface of your CD's, and also use a dark marker pen to run along the outside edge. Both of those things were said to reduce read errors and hence enhance the sound)
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Post by Deleted on Apr 8, 2016 11:06:46 GMT
Well, I ripped my entire CD collection to a Synology NAS drive using dBpoweramp. That has a feature called AccurateRip, which compare an 8 Byte CRC for each track with a database of all other rips of that track. If the CRC is identical to other rips then the rip is bit perfect with all others. The software says how many rips it has compared with (up to 200 maximum) and whether your rip is accurate (ie has the same checksum) as compared with all other rips.
The main ones that caused errors were ones I had done things to, like cleaning to get rid of mould release agent etc. Cleaning with washing up liquid would often get the rip accurate, and in some cases polishing scratches out of the surface using Duraglit. In one extreme case with a really deep scratch on an unobtainium disc I took the scratch out with 1000 grit wet and dry, then polished the dull surface back with duraglit. After which perfect rip.
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Post by Stratmangler on Apr 8, 2016 14:41:35 GMT
Well, I ripped my entire CD collection to a Synology NAS drive using dBpoweramp. That has a feature called AccurateRip, which compare an 8 Byte CRC for each track with a database of all other rips of that track. It's interesting when you use dbPoweramp and the CD isn't on the database dbP references to. I have have a few such instances - the last memorable one was the Nile Rodgers/Chic Organisation double CD of a couple of years ago, which didn't have any reference entries on freedb, so I had to enter all the metadata myself. The CDs were accurately ripped - 2 read sweeps were made, and there was an immediate check that the read data was identical, so I know that the rips are secure. Another instance was just last night - I had a low volume sales CD sent over from the States, and it too did not exit on freedb (it still doesn't, and won't for another month). This is the CD - it's a good EP too. The guitarist and the bassist were in Cry Of Love, and also the Black Crowes, amongst others ...  |
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Post by Stratmangler on Apr 8, 2016 15:06:44 GMT
With regard to the 24K gold CDs - the only thing that would make them sound better than bog standard aluminium foil pressed CDs is the production mastering.
If you analyse rips of such material you'll generally find that the Gold CDs have much lower levels than the standard production CDs, and the Gold ones are generally released on audiophile labels.
One thing that would not occur with a Gold CD that has not been edge sealed properly is CD rot - gold is one of the most inert materials available, whereas aluminium is somewhat more volatile.
The whole CD rot thing was because PDO Blackburn didn't pay proper attention to manufacturing process, and didn't edge seal the discs properly, resulting in the aluminium foil layer being open to air borne and handling contaminants, and the foil literally rotted in its substrate.
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Post by Deleted on Apr 8, 2016 16:35:51 GMT
With regard to the 24K gold CDs - the only thing that would make them sound better than bog standard aluminium foil pressed CDs is the production mastering. If you analyse rips of such material you'll generally find that the Gold CDs have much lower levels than the standard production CDs, and the Gold ones are generally released on audiophile labels. One thing that would not occur with a Gold CD that has not been edge sealed properly is CD rot - gold is one of the most inert materials available, whereas aluminium is somewhat more volatile. The whole CD rot thing was because PDO Blackburn didn't pay proper attention to manufacturing process, and didn't edge seal the discs properly, resulting in the aluminium foil layer being open to air borne and handling contaminants, and the foil literally rotted in its substrate. Interesting. But it isn't anything as robust as foil. After injection moulding the disc, aluminium (or gold) is sputtered onto the moulded surface. Only about 10 - 20 nanometers is evaporated on, and if so thin if you hold it up to a strong light, you can see though it. Some CD's are very thin indeed and you can clearly see through them, others are nearly opaque. The thin layer is then capped with about 0.25 - 0.5mm of protective lacquer with the printing on it. The surface of the metal is far from flat - any evaporated layer goes down as an island film initally, and then as the layer is built up the islands join up and leave a bumpy surface - so when you look at such a layer under a microscope you can clearly see this. Same thing happens with aluminium *and* gold. Put into those contexts it is a wonder the medium actually works at all! |
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