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Boston Audio Society The BAS Speaker Magazine
CD-R Errors -- A Worrisome Trend
Article By E. Brad Meyer
The BAS Speaker Volume 31 No. 2

 

The Problem
A fair amount of the work I do these days at my company, Point One Audio, involves transcribing older formats to CD-Rs. People bring me their family memories old stories, taped letters to kids, musical performances by parents now in their dotage on 78s, LPs, reel-to-reel tapes and cassettes. I play them into Pro Tools and use plug-ins to remove ticks and pops, hum, buzz and some of the broadband noise, and record the results on CD-Rs. It's a fairly expensive proposition for most people, so they don't get it done unless the recordings are important to them. Often I make multiple copies that are distributed to the family for the holidays.

For a long time I assumed that what I had given my customers was a final product. Optical discs are supposed to last a long time, even if Sony's early CD slogan, "Perfect Sound, Forever", had become an object of derision among high-end writers. The scoffers were mocking the "perfect"; nobody was arguing with "forever". Some of the old 12 video laserdiscs developed a problem known as laser rot after a few years because the disc was made by gluing two halves together and the seal went bad at the edge, allowing oxygen to combine with the reflective layer. CDs were supposed to be immune to such things.

Reports in the consumer press, though rare, seemed to confirm the CD's longevity and low error rate. David Ranada, writing for Stereo Review during the mid-1980s, tapped into the error-correction circuits of his CD player and reported that an ordinary disc, subjected to ordinary handling for a few months, would still play with manageably few corrected errors and no uncorrectable ones.

It was with dismay, therefore, that I heard last year that some CD-Rs I had made of old family tapes refused to play without skipping or stopping in some CD players. As I started to track this down I found that some players do not age well. The ones I bought in the earliest days of the format, including a my original Sony CDP-101 and a Technics model with a slider that varies the playback speed over 6 percent, have all failed, and parts seem no longer to be available. A ten-year-old Denon three-CD changer (part of a compact stereo stashed out of sight in a room whose decor is from an earlier time) also began behaving erratically and has now, as we used to say at my college radio station, crumped.

But some of the problem seemed to be traceable to the blank CD-Rs I had used, some of which were generic 80-minute data blanks bought at Micro Center in Cambridge or, when I didn't feel like driving in there, at Staples.

 

The Diagnosis
Customers were unable to play my CDs, and that's an issue for me whatever the source of the problem. I needed a way to analyze the quality of the CD-Rs I was burning. Fortunately I recently had an old friend put together a new office PC for me, including a Plextor CD/DVD burner and a copy of a utility program called Plextools Professional LE (which I understand has now become hard to get). Plextools will analyze an entire audio CD in about four minutes, giving readouts of three types of errors: C1, C2 and CU. C1 and C2 errors are in theory correctable, meaning that before the D/A conversion the original data are totally restored. CU errors cannot be completely corrected and require the player to interpolate the audio signal, which in effect means to take a good guess at what it should be in the hope that there will be no audible effect.

The knowledge afforded by Plextools is a mixed blessing. It is very nice, for starters, to be able to know a disc I have made is good, because I can now include the low error numbers when I send a master to a pressing plant for commercial production. I have had a plant refuse to press a disc, and demand a free replacement, when their error-rate program showed unacceptably high numbers at the outer edge. They supplied a chart showing this but ignored my request that they ship the disc back to me. Clearly, from the pattern, someone had grabbed the thing improperly and left a big finger-print on the edge, but I couldn't prove that. Now I can. Plextools reports the three types of errors each in three ways: average per second, maximum per second, and total errors for the disc. On a good newly copied CD-R blank, the C1 errors average about30/s, with a maximum per-second rate of 50, and there are no C2 or CU errors on the entire disc.

The down-side, at least at first, was learning about what seems to be happening to my CD-Rs over time. Someone recently brought a two-CD project back so I could make some more copies. The originals, made in2001, showed very high C1 error rates, well over 500/s toward the outer edge (these discs appeared to be clean under strong reflected light), with a few hundred C2 errors per second and even a fair number of CUs. All of these rates increased from inside to outside (that is, they were the worst near the end of the audio program). My aging JVC consumer player shows audible effects (in the form of raspy noise modulation) from these error rates. Fortunately my HHB CD recorder has superior error correction and concealment, and plays both discs acceptably, so I was able to make copies without audible problems. (A more recent purchase, the Yamaha DVD-S1500 high-bit player, also sounds good with these older CD-Rs.)

I recently ran a test on a copy of the BAS test CD that was burned in2007. The C1 rate starts at 250/s and climbs to a maximum of 4106/s (average for the disc is 2421/s); C2 errors start to appear about 15 minutes in and climb from there, with an average over the disk of 61/s and a maximum of 289/s. CU errors appear about 35 minutes in, averaging 16/s for the disc and reaching a maximum of 269/s. The maximum CU error rate occurs during the high-level multi-tone (track 25) which on my JVC consumer player has audible crackles. The HHB CD recorder plays it cleanly.

I can verify that commercial pressed CDs are indeed most often free of audible data errors, even when handled with only moderate care. I tested a disc I've used many times to demonstrate my system's ability to use the information encoded in the Q-sound process to generate surround material from only two speakers (Amused to Death by Roger Waters, Columbia CK 47127). Plextools reported average C1 errors of15.9/s, a maximum of 55.0/s and a total of 69,234 for the 72-minute disc. There are C2 errors on this disc too: 0.5/s on the average but 153/s maximum. The C2 total is only 2042. There is a graph of the three types of error, displayed as green, blue and red, versus time. This chart (which the program unfortunately will not export) shows a broad band of more or less constant C1 errors, with a spike of blue C2 errors at the 50-minutemark. There is a light circumferential scratch on the disc at what looks like that point, and even small imperfections can cause trouble if they block the laser for more than a few degrees of rotation. (A brief attempt to clean that part of the disc by rubbing it from center to edge did not improve things.)

 

A Solution Of Sorts
I am not the only one to have noticed these effects. The general article on the audio CD in Wikipedia (http://en.wikipedia.org/wiki/Compact_Disc) says, in part, "CD-R recordings are designed to be permanent. Over time the dye's physical characteristics may change, however, causing read errors and data loss until the reading device cannot recover with error correction methods. The design life is from 20 to 100 years, depending on the quality of the discs, the quality of the writing drive, and storage conditions. However, testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions...This failure is known as CD rot."

I have found that CD-R blanks vary widely in quality even right after they are burned. There are two types of dye commonly used and the cheaper one does give inferior results. But even within a single batch of discs, the error rate varies; one might have an average C1 of 32/s and the next one in the stack will come out at 80 to 100. And these tests are run right away, so they don't predict how long it will be before things start to deteriorate.

There is a very expensive Memorex CD-R called the Pro Gold Archival (packaged in a nasty odd-shaped plastic box that won't take normal tray cards and which you will wind up throwing away), that costs $10 for a package of three. The dye layer (the underside) is supposed to be actual gold, and it appears to be. The box says "Lasts up to 300 years". I have no way of knowing whether this is true and I dare say Memorex doesn't either. In my experience some of their cheaper blanks are of below average quality. But I might have to start using these, or a cheaper equivalent if I can find one, for treasured family memories. I'll just have to charge a little more per copy.

The longevity of masters that I send to a CD plant is not an issue; they are serving as temporary data storage devices whose content will soon be transferred to longer-lived copies. As long as their initial error rate is low, they will serve. However, something must be done about the others. I can't have someone trying to play my "archival" transcription of the time grandma sang live on NBC radio in 1948 and have the disc fail to play. I'm going to have to ask some of my customers to bring in the CD-Rs I've given them to see if I need to replace them with better blanks.

[Bob Miller reported that a few years ago his organization received a stack of 100 defective MAM-A Gold Archive CD-Rs. Joe Weisenbach, MAM-A engineering and quality manager, said that was likely from their manufacturing facility in France, which in 2005 went out of business, as did MAM-As corporate owners, Computer Support Italcard, of Italy. Since then MAM-A has been an independent company and has tightened control over their manufacturing and quality control activities. MAM-A (www.MAM-A.com) was originally Mitsui Advanced Media, and is based in Colorado. DJW]

 

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