User guide

BrightEye 94

BrightEye 94 - Page 25

can be very cost effective in transmission and routing, but 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 transi-

tions 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 informa-

tion 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 require-

ment 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.

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.