Ensemble Designs BrightEye 3 User manual

This user guide provides detailed information for using the BrightEye™ 3
Analog to SDI Converter with Time Base Corrector and Frame Sync.
The information in this user guide is organized into the following sections:
• Product Overview
• Functional Description
• Applications
• Rear Connections
• Operation
• Front Panel Controls and Indicators
• Using The BrightEye Control Application
• Warranty and Factory Service
• Specifications
• Glossary
BrightEye-1
Analog to SDI
Converter with
TBC and Frame Sync
User Guide
Revision 4.0 SW v1.0.8
ENSEMBLE
DESIGNS

BrightEye 3 Analog to SDI Converter with TBC/FS
PRODUCT OVERVIEW
The BrightEye™ 3 Converter is a Time Base Corrector/Frame Synchronizer with
composite, component and Y/C inputs. Input signals are digitized to 12 bits of res-
olution and time base corrected by a noise tolerant tracking circuit. An external
reference input allows genlock to a a timing reference such as color black.
BrightEye 3 is great for such applications as capturing consumer VCRs into non-
linear editing systems.
Input selection, gain controls, and TBC enable is provided through the front panel
interface. Input and reference presence are indicated through front panel LEDs.
Control and monitoring can also be done using the BrightEye Control application
from a personal computer with USB support.
Signal I/O and power is supplied to the rear of the unit. It is powered by a
modular style power supply.
A glossary of commonly used video terms is provided at the end of this guide.
FUNCTIONAL DESCRIPTION
The BrightEye 3 converter can perform analog to digital conversion on a variety
of television signal formats, in both the 525/60Hz (NTSC) and 625/50Hz (PAL)
line standards. The converter supports the NTSC and PAL composite standards,
Y/C, and color difference analog component formats along with serial digital (SDI)
video.
As shown in the block diagram on the next page, analog composite video is fed to
the converter on a single BNC connector at 1 volt p-p levels (sync tip to peak
white). The analog signal is clamped (DC restored) and digitized. This digital rep-
resentation of the original signal is decoded into luminance and color difference
component form using an adaptive comb filter.
Component video inputs in the SMPTE or Beta formats of Luminance (Y), and
color difference (R-Y or Pr, and B-Y or Pb) enter the converter through three BNC
connectors. They are digitized and clamped and then gain-scaled to component
digital levels.
In all cases of analog video input, the resultant digital signal conforms to the
ITU-R 601 standard. This is a 4:2:2 component digital signal with a 27 MHz
sampling rate. The overall amplitude of the signal can be adjusted with the gain
control. This digital signal is fed to the TBC/Frame Synchronizer.
BrightEye-2

The TBC/Frame Synchronizer performs time base correction and synchronization
on its input signal (either analog or digital) to conform its timing to the house
reference provided on the external reference input (Ref In). This synchronizing
function will automatically align the timing of the converter output so that each
new video frame begins at exactly the same time as it does on the reference
input. Furthermore, since the original input to the converter may be non-syn-
chronous to the reference, the input video may be running slightly fast or slow
with respect to the reference. The synchronizer corrects for this by buffering the
signal through a memory FIFO which can hold up to one frame of video.
The output of the TBC/Frame Synchronizer is serialized as a 270 Mb/s bitstream
and feeds the electrical BNC connector.
BrightEye 3 is powered by a 12 volt DC universal power supply. This power
supply can accept an input voltage between 90 and 230 volts, at 50 or 60 Hertz. It
uses a standard IEC line cord and can be used anywhere in the world. It is
normal for the converter to be quite warm to the touch when operating.
BrightEye-3
Bar
Generator
12-bit
Video A-D
Converter
and
Decoder
SDI
Deserializer
SDI Out
Reference In
Cpst, Y In
Pr, C In
Pb
TBC/
Frame Sync Serializer
Video Select
TBC On/Off
Processing
Controls
Gain Adjust
Front Panel or BrightEye PC Controls
Proc
Amp
BrightEye 3 Functional Block Diagram

BrightEye 3 Analog to SDI Converter with TBC/FS
APPLICATIONS
The versatility of BrightEye 3 can be utilized in any number of different applica-
tions where conversion of composite/Y/C and component analog video to SDI is
required.
Analog to SDI/Optical Conversion and Distribution
One application, shown in the illustration below, utilizes the full functionality of
BrightEye 3 by converting an output from a consumer VCR to an SDI signal for
feeding a non-linear editing system. The use of a reference input also allows the
converted signal to be synchronous with the house reference.
BrightEye-4
BrightEye 3
House Ref
Non-Linear
Editor
SDI Out
Cpst In
Ref In
Consumer
VCR
BrightEye 3 Application

REAR CONNECTORS
All connections to the BrightEye converter are made on the rear of the unit.
Refer to the illustration below.
Power Connection
Connect a modular power supply to the 12 volt DC power input connection on the
far left. Use the locking ring to secure it.
USB Connector
The USB connector is used to provide more comprehensive control, diagnostics,
and upgrades to the unit from a PC or Mac. Use the BrightEye Control applica-
tion included on CD-ROM to make adjustments as described in the OPERATION
section of this user guide.
Input/Output BNCS
There are five rear BNC connectors which are used as follows:
SDI Out
The Serial Digital Component output of the converter is presented on this
connector. This output conforms to the ITU-R 601 standard for serial digital
video, with SMPTE 259M serialization at 270 Mb/s.
Pb In
This is an internally terminated, 75 ohm input for the following:
• Beta or SMPTE – Pb input
Pr, C In
This is the internally terminated, 75 ohm input for the following format signals:
• Beta or SMPTE – Pr (Y-R) input
• S-Video (composite) – C input
BrightEye-5
BrightEye 3 Rear Connectors

BrightEye 3 Analog to SDI Converter with TBC/FS
BrightEye-6
Cpst, Y In
This is the internally terminated, 75 ohm input for one of the following signal
formats:
• Composite (Cpst) – composite input
• S-Video (composite) – Y input
• Beta or SMPTE – Y input
Ref In
The reference input connector accepts a composite video signal which is used as
the genlock and timing reference for the internal TBC/Frame Synchronizer.
Typically the reference signal would be Color Black or Color Bars fed from a
master sync generator. This is an internally terminated 75 ohm input.

BrightEye-7
OPERATION
Control and operation of the BrightEye 3 converter is performed from the front
panel or with the BrightEye Control application.
Some control settings are only available with BrightEye PC or Mac. These parameters
cannot be monitored or controlled with the front panel.
Front Panel Controls and Indicators
The front panel of the converter, shown in the figure below, provides status indi-
cators and control over video input selection, TBC, and gain.
Status Indicators
The following status indicators are provided on the front panel:
In
Illuminates green when an input for the currently selected video format is
detected on the input connector. This indicator does not light when either of the
two internally generated test patterns are selected.
Ref (Reference)
Illuminates green when a reference video signal is present on the Ref In
connector.
Source Select
The currently selected video input will illuminate green.
TBC/Frame Sync
When illuminated green, the TBC/Frame Sync mode is enabled.
Gain
Illuminates green when gain is set to unity or red when gain is other than unity.
Pwr (Power)
Illuminates green when power is applied to the converter and the internal voltage
regulator is functioning correctly.
BrightEye 3 Front Panel
NOTE:

BrightEye 3 Analog to SDI Converter with TBC/FS
BrightEye-8
ADJUSTING PARAMETERS FROM THE FRONT PANEL
Use the Mode, Right Arrow, and Left Arrow buttons to select and adjust
parameters from the front panel.
Pressing the Mode button activates the front panel for editing and tabs between
each section of editable parameters.
Pressing the Right Arrow or Left Arrow advances the selection within a given
section of parameters, or increases (Right Arrow) or decreases (Left Arrow) the
value of a selected parameter.
The LED of an edited parameter will blink for 15 seconds, after which time its value is
stored in memory. If power is interrupted before this 15 second timeout period has
elapsed, the edited state will not be not saved.
The controls and their indicators are described below:
Source Select Mode
This control selects the video input with the following choices:
Cpst – Analog Composite Video
Y/C – S-Video Composite Video
Beta – Component Video in Beta format
SMPTE – Component Video in SMPTE format
Bars – Selects internal Color Bar Generator
ChkFld – Selects internal CheckField Generator
The green indicator under the selected source will be illuminated.
TBC/Frame Sync Mode
This control turns the TBC/Frame Sync function on/off. Use the left arrow to turn
it off, the right arrow to turn on. The indicator illuminates green when it is on.
Gain Mode
This control adjusts the overall gain of the analog video signals passing through
the converter. The right arrow will increase the gain, the left arrow will decrease
it. The indicator will illuminate green when the gain is set to its nominal or unity
setting. This is the setting which will produce correct digital output levels from
an analog input source which itself is at proper level. The indicator will show red
whenever the control is adjusted either higher or lower than the nominal setting.
The gain can be reset to nominal (green) by pressing both arrows simultaneously.
NOTE:

BrightEye-9
USING THE BRIGHTEYE CONTROL APPLICATION
The BrightEye PC and BrightEye Mac applications included on CD-ROM are
designed to allow you to configure and control the BrightEye 3 from a personal
computer. Installation and instructions for using this software application are
given in the PDF manual on disk. If the BrightEye 3 is connected to a computer
running this software, the following menus are available for controlling and mon-
itoring the unit.
Input Menu
• Input – select the type of input signal to the unit from the Input pulldown
as Composite,Y/C, Beta, SMPTE, SDI, Bars, or Checkfield.
• Comb Mode – use this control set the type of comb filtering desired from
3-Line or 5-Line.
• Setup Removal – use this control to indicate the presence of setup on the
input (in 525 mode only, grayed out in 625). Select On for setup removal or
Off for no setup removal.
• Signal Mute – the signal muting control affects the behavior of the module
when the video input (either analog or SDI) is lost or interrupted. Set the
control for one of the following conditions:
No Muting – nothing is done when the input is lost or intermittent. In this
case, the module may present a very disturbed output in response to an
intermittent input.
Mute on Noise – the output will go black if the input is lost.
Mute on Freeze – the output will freeze on the last image when the input
is lost.

BrightEye 3 Analog to SDI Converter with TBC/FS
The following status items are also reported for the unit:
• Input Pres – reports the presence and detected line rate of the video input.
•Ref Pres – reports the reference input status.
Proc Menu
A video processing amplifier allows the adjustment of parameters for the analog
input signal.
The Proc menu provides the following video processing controls:
• Gain – adjusts the overall gain of the analog video signals passing through
the converter from 50 to 150%. The front panel indicator will light green
when the gain is set to its nominal or unity setting.
This is the setting which will produce correct digital output levels from an
analog input source which itself is at proper level. The indicator will show
red whenever the control is adjusted either higher or lower than the
nominal setting.
• Chroma – adjusts the percentage of chroma from 50 to 150%. There is no
front panel control or indication of this setting.
• Pedestal – adjusts the pedestal level of the signal +/- 5 IRE.There is no
front panel control or indication of this setting.
•Hue– adjust the amount of hue +/- 90 degrees in 525 mode only. There is
no front panel control or indication of this setting.
All values can be reset to nominal by selecting the Default button next to
the control.
BrightEye-10

Trims Menu
The Trim menu provides the adjustments below for the component Cr and Cb
input video input gain and DC offsets to compensate for incorrect levels on the
input sources:
• Cr Gain – adjusts the input gain of the Cr channel video (± 30).
• Cb Gain – adjusts the input gain of the Cr channel video (± 30).
• Cr Offset – adjusts the DC offset of the Cr channel.
• Cb Offset – adjusts the DC offset of the Cb channel.
BrightEye-11

BrightEye 3 Analog to SDI Converter with TBC/FS
Timing Menu
Timing adjustments can be made when the Frame Sync function is enabled on
the unit.
The Timing menu provides the following controls:
• Ver Time – adjusts the vertical timing of the signal in +/- 625 line incre-
ments relative to the reference input when Frame Sync is enabled (on).
There is no front panel control or indication of this setting.
• Hor Time – adjusts the horizontal timing of the signal in +/- 1715 clock
increments relative to the input reference when Frame Sync is enabled
(on).There is no front panel control or indication of this setting.
• V Blanking – set vertical blanking to Wide (PAL Lines 1-22 and NTSC
Lines 1-20) or Narrow (PAL Lines 1-6 and NTSC Lines 1-9). There is no
front panel control or indication of this setting.
• Frame Sync – turns the Frame Sync function on or off with the menu
pulldown.

WARRANTY AND FACTORY SERVICE
Warranty
Ensemble Designs, Inc. warrants this product to be free from defect in material
and workmanship for a period of five years from the date of delivery. During this
two year warranty period, Ensemble Designs, Inc. will repair any defective units
at Ensemble’s expense if the unit should be determined to be defective after con-
sultation with a factory technician.
This warranty is not transferable. Any implied warranties expire at the expira-
tion date of this warranty.
This warranty does not cover a defect that has resulted from improper or unrea-
sonable use or maintenance as determined by us. This warranty is void if there is
any attempt to disassemble or adjust factory set presets without factory autho-
rization.
Factory Service
If you require service (under warranty or not), please contact Ensemble Designs
and ask for Customer Service before you return the unit. This will allow the
service technician to provide any other suggestions for identifying the problem
and recommend possible solutions.
You may also refer to the technical support section of the Ensemble web site for
the latest information on your equipment at the URL below:
http://www.ensembledesigns.com/support
If you return equipment for repair, please get a Return Material Authorization
Number (RMA) from the factory first.
Ship the product and a written description of the problem to:
Ensemble Designs, Inc.
Attention: Customer Service RMA #####
870 Gold Flat Rd.
Nevada City, CA 95959 USA
[phone]
Fax: [phone]
[email protected]
http://www.ensembledesigns.com
Be sure to put your RMA number on the outside of the box.
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BrightEye 3 Analog to SDI Converter with TBC/FS
SPECIFICATIONS
Analog Input:
Number: One
Type: Beta/SMPTE, Y, Pr, Pb
NTSC, PAL Composite
NTSC, PAL S-Video
Impedance: 75 Ω
Return Loss: > 40 dB
Input DC: +/- 1 volt DC
Input Hum: < 100 mV
Serial Digital Output:
Number: One
Type: 270Mb/s SD Serial digital
(SMPTE 259M)
Impedance: 75 Ω
Return Loss: > 15 dB
Output DC: None (AC coupled)
Analog to SDI Performance:
Bit Resolution: 12 bit input quantization
4 X oversampling
Signal to Noise: > 62 dB, weighted
Frequency Response:
Composite and Y ± 0.1 dB, 0 to 5.5 MHz
Pr, Pb ± 0.1 dB, 0 to 2.75 MHz
Minimum Delay: 90 µSec
Reference Input:
Number: One
Type: 1 V p-p Composite Video
PAL or NTSC
Impedance: 75 Ω
Return Loss: > 40 dB
General Specifications:
Size: 5.625” W x 0.8 “ H x 5.5” D
(143 mm x 20 mm x 140 mm)
including connectors
Power: 12 volts, 7 watts
Temperature Range: 0 to 40 degrees C ambient
Relative Humidity: 0 to 95% noncondensing
Due to ongoing product development, all specifications are subject to change.
BrightEye-14

BRIGHTEYE POWER SUPPLY INFORMATION
Below is a list of power supplies and optional items that may have come with your
BrightEye:
BEPS
BrightEye Individual Power Supply.
BEPS6
Spider Power Supply. This powers 6 single high BrightEyes or 3 double high
BrightEyes (BrightEye 90 family).
BEPS6-RP
Redundant Power Supply for Spider.
BERKMT
BrightEye Rack Mount. This holds 6 single high BrightEyes or 3 double high
BrightEyes (BrightEye 90 family) or a combination.
BEBP
BrightEye Blank Panel. Single high, for empty slots in Rack Mount.
BEAC
Analog Audio Breakout Cable.
BrightEye-15

BrightEye 3 Analog to SDI Converter with TBC/FS
GLOSSARY
This is a brief glossary of commonly used terms associated with this product.
AES/EBU
The digital audio standard defined as a joint effort of the Audio Engineering
Society and the European Broadcast Union. AES/EBU or AES3 describes a serial
bitstream that carries two audio channels, thus an AES stream is a stereo pair.
The AES/EBU standard covers a wide range of sample rates and quantizations
(bit depths.) In television systems, these will generally be 48 KHz and either 20
or 24 bits.
Bandwidth
Strictly speaking, this refers to the range of frequencies (i.e. the width of the
band of frequency) used by a signal, or carried by a transmission channel.
Generally, wider bandwidth will carry and reproduce a signal with greater
fidelity and accuracy.
Beta
Sony Beta SP video tape machines use an analog component format that is
similar to SMPTE, but differs in the amplitude of the color difference signals. It
may also carry setup on the luminance channel.
Blanking
The Horizontal and Vertical blanking intervals of a television signal refer to the
time periods between lines and between fields. No picture information is trans-
mitted during these times, which are required in CRT displays to allow the
electron beam to be repositioned for the start of the next line or field. They are
also used to carry synchronizing pulses which are used in transmission and
recovery of the image. Although some of these needs are disappearing, the
intervals themselves are retained for compatibility purposes. They have turned
out to be very useful for the transmission of additional content, such as teletext
and embedded audio.
CAV
Component Analog Video. This is a convenient shorthand form, but it is subject to
confusion. It is sometimes used to mean ONLY color difference component
formats (SMPTE or Beta), and other times to include RGB format. In any case, a
CAV signal will always require 3 connectors – either Y/R-Y/B-Y, or R/G/B.
Checkfield
A Checkfield signal is a special test signal that stresses particular aspects of
serial digital transmission. The performance of the Phase Locked-Loops (PLLs) in
an SDI receiver must be able to tolerate long runs of 0’s and 1’s. Under normal
conditions, only very short runs of these are produced due to a scrambling
algorithm that is used. The Checkfield, also referred to as the Pathological test
signal, will “undo” the scrambling and cause extremely long runs to occur. This
test signal is very useful for testing transmission paths.
BrightEye-16

Chroma
The color or chroma content of a signal, consisting of the hue and saturation of
the image. See also Color Difference.
Component
In a component video system, the totality of the image is carried by three
separate but related components. This method provides the best image fidelity
with the fewest artifacts, but it requires three independent transmission paths
(cables). The commonly used component formats are Luminance and Color
Difference (Y/Pr/Pb), and RGB. It was far too unwieldy in the early days of color
television to even consider component transmission.
Composite
Composite television dates back to the early days of color transmission. This
scheme encodes the color difference information onto a color subcarrier. The
instantaneous phase of the subcarrier is the color’s hue, and the amplitude is the
color’s saturation or intensity. This subcarrier is then added onto the existing
luminance video signal. This trick works because the subcarrier is set at a high
enough frequency to leave spectrum for the luminance information. But it is not a
seamless matter to pull the signal apart again at the destination in order to
display it or process it. The resultant artifacts of dot crawl (also referred to as
chroma crawl) are only the most obvious result. Composite television is the most
commonly used format throughout the world, either as PAL or NTSC. It is also
referred to as Encoded video.
Color Difference
Color Difference systems take advantage of the details of human vision. We have
more acuity in our black and white vision than we do in color. This means that
we need only the luminance information to be carried at full bandwidth, we can
scrimp on the color channels. In order to do this, RGB information is converted to
carry all of the luminance (Y is the black and white of the scene) in a single
channel. The other two channels are used to carry the “color difference”. Noted as
B-Y and R-Y, these two signals describe how a particular pixel “differs” from
being purely black and white. These channels typically have only half the
bandwidth of the luminance.
Decibel (dB)
The decibel is a unit of measure used to express the ratio in the amplitude or
power of two signals. A difference of 20 dB corresponds to a 10:1 ratio between
two signals, 6 dB is approximately a 2:1 ration. Decibels add while the ratios
multiply, so 26 dB is a 20:1 ratio, and 14 dB is a 5:1 ratio. There are several
special cases of the dB scale, where the reference is implied. Thus, dBm refers to
power relative to 1 milliwatt, and dBu refers to voltage relative to .775V RMS.
The original unit of measure was the Bel (10 times bigger), named after
Alexander Graham Bell.
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BrightEye 3 Analog to SDI Converter with TBC/FS
dBFS
In Digital Audio systems, the largest numerical value that can be represented is
referred to as Full Scale. No values or audio levels greater than FS can be repro-
duced because they would be clipped. The nominal operating point (roughly corre-
sponding to 0 VU) must be set below FS in order to have headroom for audio
peaks. This operating point is described relative to FS, so a digital reference level
of -20 dBFS has 20 dB of headroom before hitting the FS clipping point.
EDH
Error Detection and Handling is a method to verify proper reception of an SDI or
HD-SDI signal at the destination. The originating device inserts a data packet in
the vertical interval of the SDI signal and every line of the HD signal which
contains a checksum of the entire video frame. This checksum is formed by
adding up the numerical values of all of the samples in the frame, using a
complex formula. At the destination this same formula is applied to the incoming
video and the resulting value is compared to the one included in the transmis-
sion. If they match, then the content has all arrived with no errors. If they don’t,
then an error has occurred.
Embedded Audio
Digital Audio can be carried along in the same bitstream as an SDI or HD-SDI
signal by taking advantage of the gaps in the transmission which correspond to
the horizontal and vertical intervals of the television waveform. This technique
an 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 inde-
pendently of the video.
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.
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IEC
The International Electrotechnical Commission provides a wide range of
worldwide standards. They have provided standardization of the AC power con-
nection to products by means of an IEC line cord. The connection point uses three
flat contact blades in a triangular arrangement, set in a rectangular connector.
The IEC specification does not dictate line voltage or frequency. Therefore, the
user must take care to verify that a device either has a universal input (capable
of 90 to 230 volts, either 50 or 60 Hz), or that a line voltage switch, if present, is
set correctly.
Interlace
Human vision can be fooled to see motion by presenting a series of images, each
with a small change relative to the previous image. In order to eliminate the
flicker, our eyes need to see more than 30 images per second. This is accom-
plished in television systems by dividing the lines that make up each video frame
(which run at 25 or 30 frames per second) into two fields. All of the odd-numbered
lines are transmitted in the first field, the even-numbered lines are in the second
field. In this way, the repetition rate is 50 or 60 Hz, without using more
bandwidth. This trick has worked well for years, bit it introduces other temporal
artifacts. Motion pictures use a slightly different technique to raise the repetition
rate from the original 24 frames that make up each second of film—they just
project each one twice.
IRE
Video level is measured on the IRE scale, where 0 IRE is black, and 100 IRE is
full white. The actual voltages that these levels correspond to can vary between
formats.
ITU-R 601
This is the principal standard for standard definition component digital video. It
defines the luminance and color difference coding system that is also referred to
as 4:2:2. The standard applies to both PAL and NTSC derived signals. They both
will result in an image that contains 720 pixels horizontally, with 486 vertical
pixels in NTSC, and 576 vertically in PAL. Both systems use a sample clock rate
of 27 Mhz, and are serialized at 270 Mb/s.
Jitter
Serial digital signals (either video or audio) are subject to the effects of jitter. This
refers to the instantaneous error that can occur from one bit to the next in the
exact position each digital transition. Although the signal may be at the correct
frequency on average, in the interim it varies. Some bits come slightly early, other
come slightly late. The measurement of this jitter is given either as the amount of
time uncertainty or as the fraction of a bit width. For 270 Mb/s video, the
allowable jitter is 740 picoseconds, or 0.2 UI (Unit Interval – one bit width).
Luminance
The “black & white” content of the image. Human vision had more acuity in
luminance, so television systems generally devote more bandwidth to the
luminance content. In component systems, the luminance is referred to as Y.
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BrightEye 3 Analog to SDI Converter with TBC/FS
Multi-mode
Multi-mode fibers have a larger diameter core (either 50 or 62.5 microns), and a
correspondingly larger aperture. It is much easier to couple light energy into a
multi-mode fiber, but internal reflections will cause multiple “modes” of the signal
to propagate down the fiber. This will degrade the ability of the fiber to be used
over long distances.
See also Single mode.
NTSC
The color television encoding system used in North America was originally
defined by the National Television Standards Committee. This American standard
has also been adopted by Canada, Mexico, Japan, Korea, and Taiwan. (This
standard is referred to disparagingly as Never Twice Same Color.)
Optical
An optical interface between two devices carries data by modulating a light
source. This light source is typically a laser or laser diode (similar to an LED)
which is turned on and off at the bitrate of the datastream. The light is carried
from one device to another through a glass fiber. The fiber’s core acts as a
waveguide or lightpipe to carry the light energy from one end to another. Optical
transmission has two very significant advantages over metallic copper cables.
Firstly, it does not require that the two endpoint devices have any electrical con-
nection to each other. This can be very advantageous in large facilities where
problems with ground loops appear. And secondly, and most importantly, an
optical interface can carry a signal for many kilometers or miles without any
degradation or loss in the recovered signal. Copper is barely useful at distances of
just 1000 feet.
Oversampling
A technique to perform digital sampling at a multiple of the required sample rate.
This has the advantage of raising the Nyquist Rate (the maximum frequency
which can be reproduced by a given sample rate) much higher than the desired
passband. this allows more easily realized anti-aliasing filters.
PAL
During the early days of color television in North America, European broadcast-
ers developed a competing system called Phase Alternation by Line. This slightly
more complex system is better able to withstand the differential gain and phase
errors that appear in amplifiers and transmission systems. Engineers at the BBC
claim that it stands for Perfection At Last.
Progressive
An image scanning technique which progresses through all of the lines in a frame
in a single pass. Computer monitors all use progressive displays. This contrasts
to the interlace technique common to television systems.
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