Ensemble Designs 7555 HD / SD Video Processing Frame Synchronizer - Manual (Page 64)

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7555 HD/SD, 9550 3G/HD/SD, and 9550-XA 3G/HD/SD Video Processing Frame Synchronizers
can also add complexity to signal handling issues because the audio content can no longer be treated
independently of the video.
Eye Pattern
To analyze a digital bitstream, the signal can be displayed visually on an oscilloscope by triggering the
horizontal timebase with a clock extracted from the stream. Since the bit positions in the stream form
a very regular cadence, the resulting display will look like an eye – an oval with slightly pointed left and
right ends. It is easy to see from this display if the eye is “open”, with a large central area that is free of
negative or positive transitions, or “closed” where those transitions are encroaching toward the center.
In the first case, the open eye indicates that recovery of data from the stream can be made reliably and
with few errors. But in the closed case data will be difficult to extract and bit errors will occur. Generally
it is jitter in the signal that is the enemy of the eye.
Frame Sync
A Frame Synchronizer is used to synchronize the timing of a video signal to coincide with a timing
reference (usually a color black signal that is distributed throughout a facility). The synchronizer
accomplishes this by writing the incoming video into a frame buffer memory under the timing
direction of the sync information contained in that video. Simultaneously the memory is being read
back by a timing system that is genlocked to a house reference. As a result, the timing or alignment of
the video frame can be adjusted so that the scan of the upper left corner of the image is happening
simultaneously on all sources. This is a requirement for both analog and digital systems in order to
perform video effects or switch glitch-free in a router. Frame synchronization can only be performed
within a single television line standard. A synchronizer will not convert an NTSC signal to a PAL signal,
it takes a standards converter to do that.
Frequency Response
A measurement of the accuracy of a system to carry or reproduce a range of signal frequencies. Similar
to Bandwidth.
H.264
The latest salvo in the compression wars is H.264 which is also known as MPEG-4 Part 10. MPEG-4
promises good results at just half the bit rate required by MPEG-2.
HD
High Definition. This two letter acronym has certainly become very popular. Here we thought it was all
about the pictures – and the radio industry stole it.
HDCP
HDCP (High-bandwidth Digital Content Protection) is a content encryption system for HDMI. It is
meant to prevent copyrighted content from being copied. Protected content, like a movie on a Blu-Ray
disc, is encrypted by its creator. Devices that want to display the protected content, like a television,
must have an authorized key in order to decode the signal and display it. The entity that controls
the HDCP standard strictly limits the kinds of devices that are allowed decryption keys. Devices that
decrypt the content and provide an unencrypted copy are not allowed.