Writing Quality - Page 25

Calibration media

In order to ensure perfect performance and reliable test results, test players have to be regularly calibrated. Over time players get less accurate because of several influences and effects on electronics and other components.

Some examples:

• Ageing of parts like laser diodes and mechanical components (swing arm, sled)
• Distorting of optical pick-up head (influencing spot size and shape and orientation of wave front)
• Malfunctioning of components like pick-up head due to contamination and temperature changes
• Drifting of servo electronics
  

Philips test disc SBC444A

This disc has built-in defects that can be used for checking error rates. In addition to providing known errors, it tests the player under maximum stress.

On disc SBC 444A, certain results may not be perfectly repeatable because the disc stresses the player to its limits. For instance, the number of E32 errors generated by the Black Spots in particular may vary. This is because these errors are "soft errors." That is, they are caused by disturbance to the player's servo systems, rather than loss of data. Each time the disc is played, the disturbance is slightly different, and the results cannot be predicted.

Disc SBC 444A provides two kinds of defects: Missing information, and black spots. The tracks with missing information should provide fairly repeatable results since these errors are encoded into the data. The sections with Black Spots have the information in tact, but obscured by the black spots. In this case, not only is there information lost, but the servomechanisms are stressed. For example, when the readout beam encounters the black spot, focus, track following, and clock recovery servo signals disappear. After the beam has passed the black spot and the signal is restored, the pickup is out of focus, off track, and the bit clock is at the wrong frequency. This causes many additional errors to be generated in an unpredictable way.

Test Signal Disc 5B.3

The HF Test Signal Disc 5B3 is a calibration disc designed for CD disc and player manufacturers and manufacturers of CD test equipment. The disc costs $100.

Multi-point Calibration CD Disc set

The discs are intended to be used for calibration of CD test equipment. The Multi-point Calibration CD Set contains three (3) discs:

Disc 1: Predefined BLER, HF measurements.
Disc 2: Predefined radial noise, predefined radial acceleration.
Disc 3: Predefined jitter and effect length.

This three disc Philips Multi-Point Calibration Set is available from Philips Consumer Electronics, Co-ordination Office Optical and Magnetic Media Systems, Building SWA-112, PO Box 80002, 5600 JB Eindhoven, The Netherlands (fax +31 40 2732113). Cost of the complete set is US$750, Disc 1 only is available for US$275, Disc 2 costs US$325, and the price of Disc 3 is US$300, plus shipping charges. Each disc contains multiple test points recorded on a dedicated track. Tracks are separated by gaps.

• Disc 1, RCD-BH.1, contains multi-point tracks for BLER, E32, burst error length, I11/Itop, I3/Itop, Itop, push pull, cross talk, radial contrast, and asymmetry. Stable errors are created by irregular pit patterns.
• Disc 2, RCD-RA.1, provides multi-point radial noise and radial acceleration values that are generated by deviated tracks.
• Disc 3, RCD-JT.1, supports multi-point correlation for jitter and effect length (length deviation) that is controlled by modulated pit and land patterns.