JVC GR-DVA10 Technical Manual page 60

The length of sync blocks of the sub code is just 12 bytes. The sub code has the fast search function to
search the target point at a high speed. In the fast search mode, if the tape speed is increased, the angle
that the head scans the track is decreased and the form of signals that can be read by one scanning
becomes like beads on an abacus. If data of signals read by one scanning are not grouped as a sync
block, those data cannot be decoded and played back. Therefore, the length of a sync block is shortened
to secure the reproducibility of data. Since the probability to pick up the outer parity is very low in the fast
search mode, no outer parity is prepared in the sub code differently from the AUDIO/VIDEO sector. In
order to secure the reproducibility and reliability of playback data, the same data is not only written twice in
different parts of a track but also written in a half of a frame (in 5 or 6 tracks). In other words, the same
data is written over and over 10 times or 12 times in the tracks of the first half of a frame. The next data is
multiply written in the second half of the frame in the same manner, namely, written 10 times or 12 times
repeatedly.
Sync block
n u m b e r
0 1 2 3 4 5
1 7
Pre-sync
block (2)
1 8
1 9
2 0
2 1
Data-sync
block ID
(149)
Code
1 5 6
1 5 7
1 6 7
Post-sync
1 6 8
block (1)
Fig. 3-1-2 Structure of sync blocks in video sector
Sync block
number
Data-sync
block
Fig. 3-1-3 Structure of sync blocks in subcode sector
Sync Block length : 90 Byte
7 7
Byte-position number
9
VIDEO AUX (VAUX)
VIDEO DATA
VIDEO AUX (VAUX)
Outer Parity
Sync Block length : 12 Byte
Byte-position number
0 1 2 3 4 5 6 7 8 9 10 11
0
1
2
3
4
ID Sub-code
5
C o d e D A T A
6
7
8
9
10
11
3-2
8
8 1 8 9
Inner
Parity