Sony D8MM-01, Training Manual

Page: 15 / 44

13
Sub Track Information
The sub track information can be broken down into four distinct sectors.
These are called the ITI, Audio, Video and Subcode sectors. Each of
these sectors is separated by a gap. These gaps are there to allow for
small tracking errors that may occur when editing.
Each sector has its own designated purpose:
§
ITI Sector – ITI stands for Insert and Track Information. It is used to
control the tracking for insert editing. It also contains data that identi-
fies the track format. The ITI sector contains 3600 bits per sub track.
§
Audio Sector – This contains the audio information and parity bits
used for error correction. The audio sector contains 11,550 bits per
sub track.
§
Video sector – This contains the video information and parity bits
used for error correction. The video sector contains 113,225 bits per
sub track.
§
Subcode Sector – This contains an ID block which contains an index
ID, PP-ID (still picture search marker), Skip ID and absolute track
number. The data block contains subcode data for time code, REC
date and REC time. Parity information is also contained in this sector.
The subcode sector contains 3725 bits per sub track.
In addition to the sectors, there are three Gap areas between the four
sectors. They are called Gap 1, 2 and 3 and contain a preset run of bits.
These gaps contain 625, 700 and 1550 bits respectively.
If we add up the total number of bits in a complete sub track we will count
134,975 bits. Since there are ten sub tracks per frame, we have 1.35Mb
per frame. Since the NTSC signal contains 30 frames per second, we will
have a total of 40.5Mb per second.
Alternating Head Pattern
Since there is an odd number of tracks in one frame, it is important to note
that the head pattern alternates every frame. This gives us two distinct
head patterns for a frame, ABABA and BABAB. This becomes an impor-
tant fact since a bad head will cause a flickering of the picture in five
distinct bands.