GotApex? Forums - View Single Post

ArkiStan · 03-02-2001, 02:26 PM

yeah though I'm totally ignorant in this field, I'm slightly skeptical about that comment. I don't see how a laser designed for reading, and a widely used one such as a DVD laser, could ever alter the data on a disc. If it's true, you'd think people would have heard at least a slight warning by now.

ufcrusher, what do you think about the info from the FAQ list? have you read it yet? I'll copy the contents from the list: http://www.thedigitalbits.com/officialfaq.html

------------------------------------------------------

[2.4.3] Is CD-R compatible with DVD?
Sometimes. The problem is that CD-Rs (Orange Book Part II) are "invisible" to DVD laser wavelength because the dye used in CD-Rs doesn't reflect the beam. Some first-generation DVD-ROM drives and many DVD players can't read CD-Rs. The formulation of dye used by different CD-R manufacturers also affects readability. That is, some brands of CD-R have better reflectivity at DVD laser wavelength, but even these don't reliably work in all players.

The common solution is for the DVD player or drive to use two lasers at different wavelengths: one for reading DVDs and the other for reading CDs and CD-Rs. Variations on the theme include Sony's "dual discrete optical pickup" with switchable pickup assemblies with separate optics, Sony's dual-wavelength laser (to be initially deployed on Playstation 2), Samsung's "annular masked objective lens" with a shared optical path, Toshiba's similar shared optical path using an objective lens masked with a coating that's transparent only to 650-nm light, Hitachi's switchable objective lens assembly, and Matsu****a's holographic dual-focus lens. The MultiRead logo guarantees compatibility with CD-R and CD-RW media, but unfortunately, few manufacturers are using it.

Bottom line: If you want a DVD player that can read CD-R discs, look for a "dual laser" or "dual optics" feature.

An effort to develop CD-R "Type II" media compatible with both CD and DVD wavelengths was abandoned.

DVD-ROM drives can't record on CD-R or any other media. There are a few combination DVD-ROM/CD-RW drives that can write to CD-R and CD-RW. Current writable DVD drives (see 4.3) can't record on CD-R or CD-RW, although future versions will.

[2.4.4] Is CD-RW compatible with DVD?
Usually. CD-Rewritable (Orange Book Part III) has a smaller reflectivity difference, requiring new automatic-gain-control (AGC) circuitry in CD-ROM drives and CD players. CD-RW discs can't be read by most existing CD-ROM drives and CD players. The "MultiRead" standard addresses this, and some DVD manufacturers have suggested they will support it. The optical circuitry in even first-generation DVD-ROM drives and DVD players is usually able to read CD-RW discs, since CD-RW does not have the "invisibility" problem of CD-R (see 2.4.3).

Current writable DVD drives (see 4.3) can't record on CD-RW, although future versions will.

03-02-2001, 02:26 PM	#12
ArkiStan Admiral Join Date: May 2000 Location: Recession Central Posts: 5,898	yeah though I'm totally ignorant in this field, I'm slightly skeptical about that comment. I don't see how a laser designed for reading, and a widely used one such as a DVD laser, could ever alter the data on a disc. If it's true, you'd think people would have heard at least a slight warning by now. ufcrusher, what do you think about the info from the FAQ list? have you read it yet? I'll copy the contents from the list: http://www.thedigitalbits.com/officialfaq.html ------------------------------------------------------ [2.4.3] Is CD-R compatible with DVD? Sometimes. The problem is that CD-Rs (Orange Book Part II) are "invisible" to DVD laser wavelength because the dye used in CD-Rs doesn't reflect the beam. Some first-generation DVD-ROM drives and many DVD players can't read CD-Rs. The formulation of dye used by different CD-R manufacturers also affects readability. That is, some brands of CD-R have better reflectivity at DVD laser wavelength, but even these don't reliably work in all players. The common solution is for the DVD player or drive to use two lasers at different wavelengths: one for reading DVDs and the other for reading CDs and CD-Rs. Variations on the theme include Sony's "dual discrete optical pickup" with switchable pickup assemblies with separate optics, Sony's dual-wavelength laser (to be initially deployed on Playstation 2), Samsung's "annular masked objective lens" with a shared optical path, Toshiba's similar shared optical path using an objective lens masked with a coating that's transparent only to 650-nm light, Hitachi's switchable objective lens assembly, and Matsu**a's holographic dual-focus lens. The MultiRead logo guarantees compatibility with CD-R and CD-RW media, but unfortunately, few manufacturers are using it. Bottom line: If you want a DVD player that can read CD-R discs, look for a "dual laser" or "dual optics" feature. An effort to develop CD-R "Type II" media compatible with both CD and DVD wavelengths was abandoned. DVD-ROM drives can't record on CD-R or any other media. There are a few combination DVD-ROM/CD-RW drives that can write to CD-R and CD-RW. Current writable DVD drives (see 4.3) can't record on CD-R or CD-RW, although future versions will. [2.4.4] Is CD-RW compatible with DVD?** Usually. CD-Rewritable (Orange Book Part III) has a smaller reflectivity difference, requiring new automatic-gain-control (AGC) circuitry in CD-ROM drives and CD players. CD-RW discs can't be read by most existing CD-ROM drives and CD players. The "MultiRead" standard addresses this, and some DVD manufacturers have suggested they will support it. The optical circuitry in even first-generation DVD-ROM drives and DVD players is usually able to read CD-RW discs, since CD-RW does not have the "invisibility" problem of CD-R (see 2.4.3). Current writable DVD drives (see 4.3) can't record on CD-RW, although future versions will.