Frequently Asked Questions About Compact Discs

Please contact Media Sciences if your questions are not answered on these pages.

ISO, ECMA, and ANSI Standards for diskettes designate PTB Reference Material. CD-ROM Standards do not. Why?

Standards committees for diskettes wisely selected a neutral government laboratory, the Physikalisch-Technische Bundesanstalt (PTB), to provide Reference Material for diskette parameters. PTB also provides magnetic card stripe reference material. A gap remained for diskette linearity and for missing bit and extra bit errors. There are no neutral third party providers of reference material for other interchangeable mass storage media such as QIC tape, helical scan tape, and optical discs. Public Reference Material from PTB remains the exception, not the rule.

Philips and Sony jointly developed private compact disc standards such as the Red Book for CD- DA, the Yellow Book for CD-ROM, and the Orange Book for CD-R. Public Standards appeared later including IEC 908 for CD-DA, ISO 9660 for the CD-ROM format, and ISO/IEC 10149 for CD-ROM interchange. No provision was made for reference material.

Philips designed test discs so that CD media and drive manufacturers can coordinate their designs. These discs can also be used to support correlation between testing facilities. Philips Signal Test Disc 5259 was the original reference for Red Book digital audio. Philips Test Sample 5 was made available in 1986 to support Red Book and Orange Book tests. Test Sample 5B.2 provides the same support but from a new stamper.

Test Sample 5B.2 provides references for I11, I3, asymmetry, crosstalk, and push-pull CD-DA, CD-ROM, and CD-R tests. Orange Book reflectivity and radial contrast tests are also supported by 5B.2, plus reference values of jitter and length deviation for all legal pit and land lengths.

Philips also designed playability disc SBC 444A so that drive manufacturers can stress their pickup and servo designs. This disc contains three types of defects of various durations that disrupt radial, focus, and spindle servo circuits, thereby either creating or lengthening errors related to these defects.

Disc SBC 444A contains three types of intentional defects having predictable and reproducible properties. Interruptions are the first type, and are recorded imperfections that simulate scratches. Good drives should be able to correct errors arising from these regions. E22, E32, and BURST should be zero as the interruptions regions step between 400, 500, 600, 700, 800, 900, and 1000 micrometers. These interruptions may generate uncorrectable errors in drives with poor pickups or servos.

Black dots having diameters of 300, 500, 600, and 800 micrometers are the second type of defect. Uncorrectable E22, E32, and BURST errors are generated by the larger dots. Proper servo and pickup designs are confirmed by a small number of errors. The third defect type is a large, simulated fingerprint that should not generate uncorrectable errors.

Philips disc SBC 444A can be used as an error reference disc. Error rates in the interruption, black dot, and fingerprint regions can be used to confirm the stability of a test drive. E22, E32, and BURST error rates for the black dots can be calculated and compared to measured results. Results from high quality test drives will slightly exceed calculated values because of practical servo and pickup limitations. Poor quality drives will generate much higher error rates.

Philips 5B.2 and SBC 444A provide a proven and accepted basis for correlation. These discs should be available through your test equipment provider. Single point calibration only provides correlation for values near that point. Studies have shown poor correlation when parameters depart significantly from the 5B.2 values. Unfortunately, this lack of correlation can exist at specification limits. Measurements at one facility might pass the disc while tests at a different location could fail the same disc. Although an obvious solution is to make discs that are well within the specification limits, efforts have been made to generate linearity test discs that would support multiple-point correlation.

Philips and Sony developed a three disc Multi-Point Calibration Set for that purpose. 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 are controlled by modulated pit and land patterns.