Section 5. Advanced Features and PlexTools Professional
PX-716 Installation and Users Manual 89
What the Histogram Means
The histogram gives a graphic representation of jitter—that is, the
variation of the 3T segment, the 4T segment, etc. The test measures the
time intervals between each two successive pit/land transitions and
compares them with DVD specifications. The test is done on a specific
area (inner, middle, or outer) of the disc.
A DVD has a total of 10 different pits, including nine from 3T to 11T
and one 14T pit. These histograms show the degree of jitter occurring at
each pit. An ideal condition (when jitter is small) is when the adjacent
pit/land peaks are thin, long and clearly separated from each other.
Figure 44:Q-Check TA Test on a poor-quality disc
A better quality disc will have histograms in which the peaks are
narrow, indicating less variation in length deviation. Also, in a good disc
there will be no peak shift—that is, peaks will lie along the green axes.
If the frequency distribution of the lands and pits seems “muddy,” or the
segments run together, the disc quality is not good.
