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BrightEye 91
BrightEye 91 - Page 31
can be very cost effective in transmission and routing, but can also add complexi-
ty 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.
HDMI
The High Definition Multimedia Interface comes to us from the consumer
marketplace where it is becoming the de facto standard for the digital
interconnect of display devices to audio and video sources. It is an uncompressed,
all-digital interface that transmits digital video and eight channels of digital
audio. HDMI is a bit serial interface that carries the video content in digital
component form over multiple twisted-pairs. HDMI is closely related to the DVI
interface for desktop computers and their displays.
