On Sat, Apr 24, 2010 at 03:52:16PM -0700, Ken Restivo wrote: No that's not how it works. Simplifying things as bit, on a real 'stamped' CD the pits should be 1/4 wavelength deep, so that the reflection of the bottom is in antiphase with the one from the surface, this provides the best 'contrast'. Writeable CDs don't have pits, either the color or the reflectivity of the surface is modified by heating it. Both require the laser power to be controlled in function of write speed. So the slowest allowed speed is not necessarily the best one. Ciao, -- FA O tu, che porte, correndo si ? E guerra e morte !

Arnold Krille wrote: From Wikipedia (http://en.wikipedia.org/wiki/CD-R#Writing_methods): "A CD recorder writes data to a CD-R disc by pulsing its laser to heat areas of the organic dye layer. The writing process does not produce indentations (pits); instead, the heat permanently changes the optical properties of the dye, changing the reflectivity of those areas. Using a low laser power, so as not to further alter the dye, the disc is read back in the same way as a CD-ROM. However, the reflected light is modulated not by pits, but by the alternating regions of heated and unaltered dye." Another (older, 2003) article I found said that there are 3 different ways of marking the track (without mentioning what the 3 different ways WERE), and the marks are called "pits" whether or not there's a pit there, an area of changed dye, or a "bubble". Non-writable optical discs use different technology. From http://electronics.howstuffworks.com/cd1.htm: "A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. We'll return to the bumps in a moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic." And continuing on to page 3: http://electronics.howstuffworks.com/cd3.htm "The elongated bumps that make up the track are each 0.5 microns wide, a minimum of 0.83 microns long and 125 nanometers high. (A nanometer is a billionth of a meter.) ... You will often read about "pits" on a CD instead of bumps. They appear as pits on the aluminum side, but on the side the laser reads from, they are bumps." So, since non-writable CD media appeared first and actually had pits/bumps, I guess it was logical to apply the same terminology to the newfangled CD-R and CD-RW media even when they don't have pits. I always thought lasers actually burned holes in the dye layer, so the scanning laser's beam would be reflected back. But, then, I always thought an interesting laser printing technology would be to use a laser that actually burnt dots on the paper (no need for toner cartridges or passing the printed page through a hot press to melt the plastic onto the paper). But neither of us have ever been found wrong in the future... ;-) -- David gnome(a)hawaii.rr.com authenticity, honesty, community

On Sat, Apr 24, 2010 at 03:52:16PM -0700, Ken Restivo wrote: It seems that the material needs a certain time to change its properties. Using faster speed but more laser power should give the same result, but sometimes is not exactly equivalent (like cooking food with much higher temperature but less time or something like that XD ), and probably the same can be said when using slow than optimal speeds, I guess. Many people everywhere recommends using very slow speeds, but I must say that personally I never noticed significant improvements with any speed. Some drives perform much better that other when extracting data. In practice is very difficult to get perfect tracks from audio cd, though tools like cdparanoia do a nice job. Digital media that can degrade the sound when dust or fingerprints are present is a nice emulation of analog media when feeling nostalgic ;) Today I just tend to write data CD or usb memories with flac files inside.