nonoise
There is a review (that I can’t locate) that explained how a laser reads the physical pits and grooves of a CD. It’s being done in an analog fashion ( a mechanical process) which then had to be processed into the digital domain.
>>>Exactly! The pits and lands are non reflective and reflective areas, respectively on the metal layer. The geometry of the pits and lands and laser assembly is such that when the CD laser beam hits a pit the reflection is canceled due to wave interference so the photodetector detects no signal. The photodetector only detects reflected signal from lands. The length of both pits and lands varies and it’s the series of various lengths of pits and lands that determines the digital information in the analog to digital converter.
Diagram 1 - CD Laser Reads Bumps (Pits Inverted) and Lands,
both of which have reflective metal surfaces. The photodetector
receives no signal from bumps, only from lands, due to destructive
interference of light waves. See last paragraph below.
Pits and Lands come in 9 different lengths, from T3 to T11.
T3 = 10001
T4 = 100001
T5 = 1000001
T6 = 10000001
T7 = 100000001
T8 = 1000000001
T9 = 10000000001
T10 = 100000000001
T11 = 1000000000001
since the spiral of pits and lands is Nano scale any vibration or wobble of the CD can force the servo mechanism to go into oscillation, producing read errors. Also the background scattered laser light gets into the photodetector, producing errors. Thus painting the outer edge of the CD Green prior to ripping will produce a better rip.