Figure 13-6.Basic videotape track system.
Most videotape recorders put at least four separate
tracks on the tape: the video track that contains the
picture information, two audio tracks that contain all
sound information, and a control track that controls the
videotape and rotation speed of the video heads
VIDEO TRACK.-When video signals are
recorded in the normal NTSC composite configuration,
one pass of the head records a complete field of video
information (Y+C). The next pass of the head, (or, if you
have a two-head machine, the second head) lays down
the second field right next to it, completing a single
video frame. Two fields make up a single frame. The
two heads must write sixty tracks (thirty frames) for
each second of NTSC video. In the four-head VTR, one
pair of heads records at normal tape speed and the other
pair records at a slower speed.
AUDIO TRACK.-The audio tracks record the
audio signal. They are usually recorded by fixed
recording heads that are near the edge of the tape and
run along the length of the videotape. Because of the
demand for stereo audio and for keeping certain sounds
separate even in monophonic sound, all VTR systems
provide at least two audio tracks.
CONTROL TRACK.-The control track contains
evenly spaced blips or spikes, called the sync pulse, that
mark each complete television frame. These pulses
synchronize the tape speed and the rotation speed of the
recording heads. This allows the tape to be played on a
similar machine without picture breakups. Because the
control track marks each frame of recorded video, it also
aids in videotape editing.
Hi8 Track System
Because space is so limited in 8mm videotape, these
systems squeeze the automatically generated time code
and other data between the video and audio portion of a
single-slanted track The time code has been developed
to provide a precise editing reference by recording the
exact frame address onto the tape. The 8mm time code
is digitally recorded by units of hour, minute, second,
and frame by the video heads. The 8mm time code is
used only for 8mm format and is not compatible with
other recording formats.
The Hi8 VTR splits each slanted track into audio
frequency modulation (AFM) and video information. It
also uses a pulse code modulation (PCM) audio track
The audio technology used in an Hi8 VTR is superior to
video home system (VHS). The video/AFM audio track
and the PCM audio track are separated by the time-code
data (fig. 13-7).
For viewing purposes, you must playback the
recording either to the transmitter or directly to a
receiver (TV set or monitor). At the receiver, the video
and audio signals are separated and processed by
separate circuitry. This circuitry changes the video and
audio signals back to sound that you can hear and
pictures that you can see. The sound is reproduced at the
loudspeaker, and the picture is reproduced on the face
of the cathode-ray picture tube.
A primary part of the monitor system is the
cathode-ray tube. A type of cathode-ray tube is used in
Figure 13-7.Hi8 VTR tracks.