MFDigital CD DVD Information Library
Tuesday, June 15, 2004
CD Manufacturing - Mastering - Laser Beam Recording
Laser Beam Recording
A Laser Beam Recorder (LBR) is used to expose the photoresist layer on the glass master where the final pits are required.
This is carried out in a class 100 controlled environment using a high power gas laser from the premastered source audio or CD-ROM data.
The laser can be blue, violet or (for DVD mastering) ultra violet. The laser beam is modulated to expose the photoresist where pits should be while the glass master spins at exactly the correct linear velocity and is moved gradually and smoothly to maintain the correct track pitch and linear velocity.
The LBR is controlled by a PC based system which formats the data from the source CD, U-matic or Exabyte tape with the CIRC error protection and EFM modulation. If an error occurs which cannot be corrected during mastering the controller will abort recording.
Speed of laser beam recording depends on the machine and input media. At one time when every CD was audio, U-matic was the only media used and only allow single speed mastering. Other newer media allow faster mastering up to 4 times, with even faster speeds possible. The following table summarises the mastering speeds for different media.
Input Media Speed Comments
U-matic (1630) 1x Still in use but is gradually being phased out. Audio data is often transferred offline to a faster format before mastering
DAT 1x Not a preferred format for mastering
CD 4x Faster if LBR capable
CD-R 4x Depends on quality of CD-R media used and speed of LBR
8mm Exabyte 8500 2.8x Max speed of Exabyte
8mm Eliant 820 4x Faster if LBR capable
Hard disk 4x Faster if LBR capable
The absolute limit of speed is dictated by the robustness of the glass. For 240 mm glass plates, the practical limit is around 6x for CD mastering.
Network mastering is a new development whereby the data content of Exabytes, CDs etc (containing the audio or othe data) is transferred to a server and mastering carried out from this data (which can be checked prior to mastering) via a high speed network. Several LBRs can be connected to the network and mastering jobs can be scheduled in advance. The result is higher speed, more reliable mastering.