Absolute Time in Pregroove
Encyclopedia
Absolute Time in Pregroove (ATIP) is a method of storing information on an optical medium, used on CD-R
and other writable discs. ATIP information is only readable on CD-R and CD-RW drives, as normal drives don't need the information stored on it.
The polycarbonate layer has a spiral pre-groove that is formed when the disc substrate is injection molded against a stamper. The read/write laser in the drive will follow this pre-groove track as it is writing, in order to maintain the spacing between the written tracks with a high degree of accuracy. This spiral has a wobble frequency
introduced into it, which the drive can read while it is writing. The drive will synchronize the rotation speed to the reference speed of the wobble signal, allowing it to maintain an accurate linear velocity (the speed of the track as it passes the laser). This wobble is further modulated with a timecode reference signal containing minutes, seconds and frames. This modulated signal is known as ATIP.
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....
and other writable discs. ATIP information is only readable on CD-R and CD-RW drives, as normal drives don't need the information stored on it.
Usage
ATIP is used as a method of putting data on an optical medium, specifically:- Manufacturer
- Writable/Rewritable
- Dye type
- Spiral length in blocks
- Rated speed
- Audio
Function
Every writable disc has at least four layers:- disc substrate - The bulk of the disc is 1.2 mm thick, and is usually injection molded from polycarbonatePolycarbonatePolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...
plastic. - Recording layer - A thin coating of dye on recordable discs, or a sandwich of metals for rewriteable discs.
- Reflective layer - A thin layer of silver, a silver alloy, or gold.
- Protective coating - a clear lacquer which is spin-coated over the top of the disc and cured with ultravioletUltravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light.
The polycarbonate layer has a spiral pre-groove that is formed when the disc substrate is injection molded against a stamper. The read/write laser in the drive will follow this pre-groove track as it is writing, in order to maintain the spacing between the written tracks with a high degree of accuracy. This spiral has a wobble frequency
Wobble frequency
DVDs and CDs have their data encoded on a single spiral, or a groove, which covers the surface of the disc. In case the optical medium is recordable, this spiral contains a slight sinusoidal deviation from a perfect spiral. The period of this sine curve corresponds to the wobble frequency...
introduced into it, which the drive can read while it is writing. The drive will synchronize the rotation speed to the reference speed of the wobble signal, allowing it to maintain an accurate linear velocity (the speed of the track as it passes the laser). This wobble is further modulated with a timecode reference signal containing minutes, seconds and frames. This modulated signal is known as ATIP.