In slightly modified form, this article was published in User Friendly the journal of the Los Angeles Computer Society in October 1997.
A quiet revolution in technology began near the end of 1995 with the release of the first practical consumer CD recorders. That revolution has been continuing as both hardware and software have evolved. By now (late 1997), do-it-yourself CDs and CD-ROMs are quite reasonable goals for the home user and are routine tools for many small offices.
A CD-Recordable (CD-R) disc differs fundamentally from a CD or CD-ROM. A 'pressed' disc is made from a glass master with the information stored as pits and lands. That master is pressed against a softened plastic aluminized to give a shiny, metallic surface which reflects the reading laser. The signal generated is very strong and unambiguous. In a CD-R, a flat plastic substrate is plated with gold and covered with a dye layer. The dye, which may be gold, green or blue, has the property that when exposed to an appropriate, strong laser light, it changes state. In one state, it is nearly transparent to infrared; in the other, it is more nearly opaque. The reading laser passes through the dye layer twice: once on the way to the gold layer, once on the way back. The resulting signal does not show as great a difference between a zero and a one as does the pressed CD, but it is still enough for most readers to decipher. The quality of the signal from a CD-R depends on the medium used, the writing laser and the reader. As a result, there is no 'best' CD-R blank or 'best' writer.
A Compact Disc Digital Audio (CDDA or CD for short) consists of a continuous stream of bits translated in a CD player into a digitized waveform which is then converted to analog for listening. Also on that disc is a Table of Contents (TOC) which consists of tiny files describing the start point and the length of the recording. They are specified in terms of recording 'blocks' on the disc; each block is 2K long and there are about 330,000 of them on a normal CD or CD-ROM. It is not important when listening to the music, but is very important when creating a CDDA to remember that the sound is not stored in files at all, but in that stream of bits. (The book of specifications for CDDA was originally bound in red and is now universally known as The Red Book; other colors apply to standards for other formats.) A redbook sound must fit the standards in detail and be recorded at 44.1 KHz sampling at sixteen bits' resolution and two channels.
A CD-ROM differs fundamentally from a CDDA in that its information is stored in conventional files of the sort familiar to computer users. One of the jobs of CD recording software is to translate a redbook bit stream into WAV files and back. Using any standard CD-R package, that conversion is transparent to the user, but for technical reasons is very important. The process of retrieving the digital bit stream from a CDDA is called Digital Audio Extraction (DAE). Not all CD-ROM readers can do DAE; some do it only very slowly, very poorly, or both; and some do it quickly and well. Therefore, not all readers are equally good at supplying information for subsequent recording if you want to make a CD-R of favorite selections from your CD library. Incidentally, the directory to the information on a CD-ROM is not stored in a FAT (File Allocation Table) or other familiar file system; it's in the TOC. One key job of the Microsoft Extensions in MSCDEX is to make the CD-ROM's TOC look like a FAT to the operating system. That's why drivers are loaded either in DOS or in Windows (or both) to enable your computer to 'see' your CD-ROM drive.
As if CDDA and CD-ROM were not enough, there are variants which mix sound and data, CD Video interactive, Photo Discs and more. Different programs support more or fewer of those formats; if you have special needs in these areas, you must find the recording package which does the job you need. There are also two major innovations in recording which may lead to new uses of CD-R when they are fully integrated in software. Packet writing allows you to dump a collection of files onto a disc when you wish but to delay building the TOC until you are ready. The other major change is the rewritable CD-R. A packet writer using a read/write (RW) will have software to mount the drive as though it were a removable hard drive or large Zip. The next step is already sampling: DVD-RAM. With that, a rewritable packet system will hold gigabytes of data!
A final warning: At this writing (September, 1997), CD-R is not a science or a solid technology. It is essentially an art form, with the advantage that once you have the formula for what you're trying to do, it tends to work repeatedly. However, the tools of that art are changing at remarkable speed. New hardware and new software emerge monthly and the truths of today will be questionable or false in a few months. However, so far it has worked well enough for me to have seen five titles pressed into 4,000 CD-ROMs - and to have at least five more projects in active development.
E-mail me at cdrecording@mrichter.com
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