Audio Engineering

Video Synchronization 813

The complete television signal is illustrated in Figures 28.1 and 28.2 , which display the signal
using two different time bases. Note the amplitude level, which distinguishes the watershed
between picture information and sync information. Known as black level, this voltage is set
to a standard 0 V. Peak white information is defi ned not to go beyond a level of 0.7 V above
this reference level. Sync information, the line or horizontal sync, 4.7- μ s pulse is visible in
the fi gure and should extend 0.3 V below the black reference level. Note also that the picture
information falls to the black level before and after the sync pulse. This interval is necessary
because the electron beam cannot instantaneously retrace to the left-hand side of the screen to

Picture

modulation

Line-sync pulse

Line

blanking

Peak video

modulation

700 mV (PAL)

0 V (black level)

300 mV (PAL)

Figure 28.1 : Television signal (viewed at line rate).

Peak video

modulation

700 mV (PAL)

0 V (black level)

300 mV (PAL)

Picture

modulation

Field

blanking

Field sync pulses

Figure 28.2 : Television signal (viewed at fi eld rate).