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. 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.
In general, error rates on good discs will be about the same at higher speeds as at 1X. Small errors such as E11 & E21 will not be affected much. Burst errors, on the other hand, will be greatly affected. Most burst errors (E22 & E32) are caused by disturbances to the servo systems, rather than missing data. This effect is greatly magnified at high speed.
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