The continuing discussion on the quality of recordable CDs has generated a huge volume of mail. The following points from H. Nakajima of West Vancouver are a valuable contribution:
"Once a CD-R [Orange Book] is burned with audio data, the disc turns into a Red Book [CD-DA] disc, which is supposed to be readable by all the audio CD players.
"Red Book specifies [among other things] the amount of laser light reflecting back from the disc surface [pitch and land] when exposed to reading laser beam spot. This is to ensure [with the given capability of photo sensor] the necessary data retrieval for servo and audio extraction.
"When CD-R was introduced some 10 years ago, it barely met the reflectivity requirement even with the use of 24-karat gold as reflector layer.
"Since then there have been improvements made in this area, but still CD-R is more "difficult" to read than regular CDs.
"There were [and still are] CD players whose reading capability was marginal. I remember when I first made in-flight audio entertainment CDs for airline companies 10 years ago, some of them did not play. It turned out that the drive in the airborne CD player was Sony's very first "cheap" Discman.
"Since the gold/green CD-R, several other types of CD-Rs have become available. All are supposed to be made under Orange Book specifications. However, there are CD-R writers [burners] which were designed before the newer discs [such as silver or blue] became available. They might not be able to burn the newer variety of discs properly.
"Today, there are many CD-R manufacturers with varying levels of experience and production capability. Product variety is so huge that quality uniformity is out of the control of Sony/Philips, the licensor.
"There still is a black-magic portion in CD-R production. If you ask CD-R drive manufacturers which disc to use for the best result, they usually give you brand names or product names they want you to use.
"One of your readers asked about his CD player's difficulty in reading inner tracks. This may well be due to the capability [optics or otherwise] of the player. But it is also possible that the disc is at fault.
"One difference between CD-R and regular CD is that CD-R has a layer of heat-absorbing dye which is applied on the surface by the spin-coating method. Although this centrifugal method is the best available to ensure a uniform layer, there is the possibility of leaving different thicknesses or other properties in different areas of the disc.
Usually, the innermost area and outermost area are more prone to quality problems, including warping. Eccentricity of the centre hole may also be a factor.
"Re: data density on tracks. This is the same anywhere on the disc. Data are laid out on the track in CLV [constant linear velocity] fashion.
"In the case with CD-R74 [650MB], the linear speed is 1.2 metres per second at 1X [audio] speed. Actual rotational speed can be as low as 200 rpm and as high as 500 rpm. [If the CD or CD-ROM is running at CAV, constant angular velocity, accessing a particular point on the surface would be much faster, since sectorizing the data area by angle is possible. But this will reduce the maximum recordable data amount]. The above is just for your information."
And reader D. Cheung also comments on the CD-R questions and comments raised in the Aug. 12 Net Works:
"Each of the people who had problems regarding the CD-Rs usually was able to fix his or her problems after switching to a 'better quality' of disc. This compelled me to search for some sort of list that would evaluate the quality of CD-Rs.
"I scoured the Net and found this: www.cdmediaworld.com/cd.htm.
This site had great reviews and also great research on the individual quality of almost every brand in the market. It's a little messy, but I think it's a great resource.
Dvorak: I agree. This is the best resource for such information I have seen.
To send John Dvorak a comment or to ask him a question, write to him at [email protected]