Clover Systems DVX-4, Руководство по эксплуатации

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Fig. 26 - “Good” DVD
INTERPRETING HF SIGNALS ON CD
I
11
This is a measure of overall signal strength. Too small of a signal makes it difficult to decode. I
11
is primarily affected
by pit depth and width. As a rule, bigger I
11
is better, and will generally produce lower error rates. Optimum I
11
is
about 0.67 on molded discs but can be significantly higher on recordable discs.
I
3
Represents the shortest pits and lands, and is the highest frequency part of the signal. I
3
is always smaller than I
11
because the smallest pits are at the limit of resolution of the optics. Pits that are too small can cause Low I
3
. Lower
writing speed (higher capacity discs) will make the pits shorter, and I
3
lower. Again, larger I
3
is better, up to a point.
Minimum allowed is 0.30, and maximum is 0.60.
Asym & Beta
Asymmetry and Beta are two different ways of measuring the same thing. They are a measure of the relative amount of
pit and land. Zero asymmetry (or beta) means that the amount of land is the same as the amount of pit. When they are
not the same, this causes distortion of the signal that makes it hard to decode.
Although they measure the same thing, Asymmetry and Beta have opposite signs in the CD specifications. So negative
asymmetry is the same as positive beta on a CD. Asymmetry for DVDs is defined with the same sign as beta (and
opposite to CDs). CDX with AMM-1 measures Beta, so we use that convention.
This measurement is useful because it is a function of the writing power of the laser during glass mastering (or writing a
recordable disc). Higher laser power produces more positive beta. Some positive beta is desirable, with optimum of
DVX Instruction Manual 41