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2–14 • System Architecture Synergy Q/MD Engineering Manual (v9.1 MD)
receiving end. This allows transmission of Progressive images via equipment that was designed to
handle interlaced images only.
Because there are no true fields in a Progressive Segmented Frame video signal, you cannot use it as a
reference signal for an Interlaced video signal.
Frequency
In the previous sections we learned that a video image is comprised of a number of horizontal scan
lines that are drawn in either a progressive or interlaced format. The length of time it takes to draw the
scan lines from the top of the screen to the bottom in a single pass is called the frequency, and is
measured in Hertz (Hz). With a Progressive scan video format this will be the time it takes to draw the
entire image. With an Interlaced video format this will be the time it takes to draw 1 field, or half, of
the image.
For example, an interlaced format of 1080i 50 Hz draws 50 fields per second. Compare this to a
progressive scan format of 720p 50 Hz which draws 50 frames per second. Notice that the interlaced
format is actually only drawing 25 frames ( Field 1 plus Field 2 ) per second, where the progressive
scan format is drawing the full 50 frames per second.
Using Frame and Field Information
Frame and Field rates become very important when you are setting up custom control pauses,
transition rates or any other system that counts a period of time in frame or fields on the switcher.
Remember from the previous section that in a progressive scan format, running at
50 Hz, the switcher
will draw 50 frames per second. In an interlaced format, also running at 50 Hz, the switcher will draw
25 frames per second.
The Synergy Q/MD switcher uses Frames to measure transition rates and custom control pauses. The
amount of time that this represents will depend on the frequency and format you are operating the
switcher in. For example, if you are operating the switcher in
1080i 59.94 Hz , the default MLE
transition rate is set at 15 Frames . Since the frequency for an interlaced format is shown in fields, you
must divide this number by 2 in order to get the number of Frames per second, 30 . By comparing the
transition rate ( 15 frames) and the video format frame frequency ( 30 frame per second) you can
calculate that the transition rate is ½ a second.
MLE Memory System Group — Transition Rate Information
Global Memory System Group — Transition Rate Information
Interlaced
Field 1
(1/50 sec at 50 Hz)
Progressive
Frame 1
(1/50 sec at 50 Hz)
REG:00 Memory0
MLE:030 KEY:008
REG:00 Memory0
M:015 D:008 F:20