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Chapter
Overview of Analog and DigitalTechnologies
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Chapter Objectives Explain the basic concepts of analog anddigital technology
Show the importance of frequency spectrumto communication along with an explanationof the concept of bandwidth
Give an overview of the interface technologybetween analog and digital technology
Describe the process of digitizing data,audio, image and video
Discuss quality retention in digitaltransmission
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Module
Overview of Analog Technology
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A
reas of A
pplication Old telephone networks
Most television broadcasting at present Radio broadcasting
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Analog Si gnals: The Basics
Cycle
Time
Signal
Amplitude
Frequency =
Cycles/Second
A typicalsine wave
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Am plitude and Cycle
Amplitude
² Distance above reference line Cycle
² One complete wave
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F requency
Frequency
²C
ycles per second² Hertz is the unit used for expressingfrequency
Frequency spectrum
² Defines the bandwidth for different analogcommunication technologies
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I nfor mation Representation
Using Analog Si gnals Information can be represented using
analog signals
Analog signals cannot be manipulatedeasily
Analog signals must be digitized for
computer processing² They must also be presented in binary
form for computer processing
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A
nalog to Di gital C onversion
1 0 1 1 0 1 0 0
A to D Converters, DigitalSignal Processors (DSP) etc.
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Data Transmission Using Analog
Technology
Digital
0s and 1s
Analog
0s and 1s
Digital-to-Analog Modulation
and vice versa
Computer Modem
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V oice Transmission Exam ple
Voice
Carrier Wave
AM Radio Transmission
Analog-to-AnalogModulation
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End of Module
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Module
Frequency Spectrum
and Bandwidth
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F
requency Spectr um
De f ined Available range of frequencies for
communication
Starts from low frequency communicationsuch as voice and progresses to highfrequency communication such as satellitecommunication
The spectrum spans the entire bandwidth ofcommunicable frequencies
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F requency Spectr um
Low Frequency High Frequency
RadioFrequency
CoaxialCable
MHz
SatelliteTransmission
Microwave MHz
Voice
KHz
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F requency Spectr um
Low-end² Voice band
Middle² Microwave
High-end² Satellite communication
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Si gnal Pr o pa gation Low frequency
² Omni-directional
High frequency (In general)² Unidirectional
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Bandwidth De f inition
Bandwidth, in general, represents arange of frequencies
300 MHz 700 MHz
Bandwidth is 400 MHz
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Usa ge of the Ter m
Bandwidth To specify the communication capacity
² A medium such as a coaxial cable isassociated with a bandwidth
To indicate the bandwidth of atechnology
² Voice grade circuits have a bandwidth of 4KHz (0-4000 Hz)
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Di gitization C onsideration Sample at twice the rate of bandwidth
for acceptable quality digitization of
voice² Sampling rate for voice transmission is
there 8000 Hz
If each sample is represented by 8-bits,the bandwidth required fortransmission is 64000 bps ²Approximately 64K bps
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C omm
unication Capacity Bandwidth is indicative of the
communication capacity
Communication speed is proportionalto bandwidth
² Shannon's law
Units used to represent bandwidth areHz, bps etc.
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C oaxial Cable Exam ple
Bandwidth of 300 MHz
C
omparison with twisted pair² Higher bandwidth
² Supports faster communication speeds
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Limiting F actors on
C ommunication Speed
Communication SpeedBandwidth Technology
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I m pact of bandwidth and Technology
on C ommunication Speed Bandwidth limitation
² Use better technology such as datacompression used in modems to increasespeed of communication
Bandwidth and technology limitation
² Move to higher bandwidth media such asfiber cables
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I m
plication Whenever a new technology with
higher communication speed is
introduced, it is first introduced on amedium of higher bandwidth² Example: Optical fiber
It is then moved to a widely usedmedium with further advancement ofthe technology² Example: Copper wire
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End of Module
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Module
An Overview of DigitalTechnology
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A
reas of A
pplication Computers
New telephone networks Phased introduction of digital television
technology
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Di gital Technology
Basics² Digital signals that could be assigned
digital values
Digital computer technology² Digital signals
² Binary representation
Encoded into ones and zeros
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Di gital A
dvanta ge Processing using computer technology
Programmable services Better quality due to being able toreconstruct exact digital patterns at thereceiving end
Faster communication speeds arepossible
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Di gital Si gnal
1 0 1 1 0 1 0 0
Pulse
TimePulse Duration
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Di gital Ter m
s Pulse
Pulse duration Pulse amplitude
Signal strength
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C lock Speed and Pulse Duration
PulseDuration
MHz
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C lock Speed and
Execution Speed Pulse duration is inversely proportional
to the clock frequency
Faster the clock speed, the smaller thepulse duration
Smaller the pulse duration, the fasterthe execution in general
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C lock Speed and C ommunication Speed
Faster the clock speed, smaller the pulseduration
Smaller the pulse duration, smaller thetime taken to transmit one bit ofinformation
Therefore, faster the clock speedmeasured in MHz, faster thecommunication speed measured in
Mbps in general
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C lock Speed and C om puter Operation
Computer operations are timed by a clock,namely by the clock speed measured in HZ
Faster the speed, the smaller the pulseduration Computer operations are timed by the pulse
duration Therefore, faster the clock speed, faster the
computer operation² A 3 GHz computer is faster than a 2 GHz
computer
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End of Module
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Module
Digital-to-Analog and
Analog-to-DigitalC
onversion
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The Need for C onversion
Analog-to-Digital Conversation² Connection of a computer to an analog
communication line
Digital-to-Digital Interface² Connection of a computer to a digital ISDN
line² Connection of different networks using a
router
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Di gital-to- Analog I nter f ace
Comp.Sys. 1
Comp.Sys. 2Modem Modem
DigitalSerialRS-232C
DigitalSerialRS-232C
AnalogITU V.90
POTS
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Di gital-to-Di gital I nter f ace
Comp.Sys. 1
Comp.Sys. 2DSLRouter DSLRouter
DigitalIEEE 802.3
DigitalIEEE 802.3
DigitalInternet
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Di gital to Di gital I nter f ace
Network 2 Network 1Router
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Di gital to Di gital I nter f ace
In general, in digital to digital interface,protocol conversion takes place² Example: Connecting an Ethernet network
to a campus backbone network using arouter
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End of Module
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Module
Overview of Digitization ofInformation
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Di gitization of I nfor mation
Information need to be digitized forcomputer processing and thetransmission of information
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C om ponents of I nfor mation
Alphanumeric data
Image
Audio
Video
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Di gital I nfor mation Pr ocessing
DataAudio
Image
Video
DigitizedandEncoded
DigitalTransmission
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The Advanta ges of Di gitization
Information can be processed by thecomputer
Easy transmission of information overthe Internet and other computernetworks
Minimize loss of quality duringtransmission
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End of Module
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The Basis
Alphanumeric data is digitized usingwell established coding systems
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C odes Used in the Di gitization
O f Data Coding Standards
² ASCII
² EBCDIC
² Unicode
ASCII Code example
² A=1000001
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The U nicode
Replaced the ASCII coding system inmicrocomputers
All variations of the Latin language
² English
² European languages
Chinese and Japanese
18 Major languages
² Eg: Tamil
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U nicode Possibilities
It is a 16-bit code as opposed to theASCII code that is basically an 8-bit
code
It is therefore possible to have 65,536variations in UNICODE
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C ommunication With ASC II And EBCD
I C
Latin languages can be transmitted incoded form
Other languages
² Bit-mapped image transmission
² Requires considerably more bandwidth
² An exception is the use of true-type fontsto display the characters of a language notsupported by ASCII
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C ommunication With U nicode
Binary encoded transmission² Latin languages
² 18 major languages
² Chinese, Japanese etc.
Transmission itself requires less
bandwidth Universal usability of software in all the
supported languages
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U nicode Advanta ge in WWW
Transm
issions
Client
TamilWebSite
Internet ExplorerBrowser retrievingTamil pages on a client
supporting Unicode.
Tamil pages are transmitted in their binary encoded form.
Site created using allthe tools such as theMS-IIS.
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Transmission of Tamil Pa ges asI m
a ges on WWW
ClientTamilWebSite
Internet ExplorerBrowser retrieving Tamilpages similar to images.
Binary image
transmission ofTamil pages.
Web pages scanned andstored as images.
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Using Downloaded F onts to H ost
and Transm
it Tam
il Pa ges
ClientTamilWebSite
Internet Explorerretrieving Tamilpages.
Site createdwith toolssuch as MS-IIS.
Download and install
theT
amil fonts.
Binary encoded form.
Bandwidth
requirements are low.
F i L W b P
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F orei gn Langua ge Web Pa geOptions
Store the page as an image
Use a font for the language, if available
Use Unicode to develop the web page
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UN I CODE Usa ge
Currently all the computers supportUNICODE
Also, the operating systems and theapplications also support UNICODE
Both hardware and software support is
necessary for the successfulimplementation of UNICODE
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End of Module
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Module
Digitization Of Audio
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Di gitization O f Audio: Overview
Take samples of audio at pre-determined time intervals known as thesampling rate
Represent the sampled audio withdigital signals
² Pulse AmplitudeModulation (PAM)
Encode signals into binary code
² Pulse Code Modulation (PCM) thatincorporates PAM as well
² Required for computer processing
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Di gitization of Audio: Pulse Am
plitude Modulation (P A M)
Audio
9 8 7 6 7 9
Digital Signals mustfurther be encodedinto binary signalsfor computerprocessing and
transmission.
Sampling Interval
Di iti ti d E di f A di
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Di gitization and Encoding of Audio:Pulse C ode Modulation (PC M)
PCM is a two step process
First the audio is sampled andrepresented by digital signals
The digital signals are then encoded inbinary form
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Binary Encoding of Si gnals in
Pulse C ode Modulation (PC M)
9 8 7 6 5 6
1001 1000 0111 0110 0101 0110
The integer numbers have effectively beencoded into zeros and ones. The ones and zerosnow contain the audio information encoded ina form that could be processed by a computer.
PCM
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Salient Points on the
Di gitization O f Audio
Sampling rate and the number of bitsused for representing the samples will
determine the quality of the audio Quality is retained in transmission
because only codes are transmitted
Audio can be recreated to the originalquality by extracting the pattern fromthe digital code
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Sam pling F actors
Sampling interval determined bysampling frequency
² Measured in Hz
Sampling depth² Measured in bits
Sampling channels² Mono or stereo, for example
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Sam pling Exam ple
CD quality audio² 44 KHz
² 16 Bits
² Stereo
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End of Module
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Module
Audio Quality, Bandwidth andStreaming
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F actors A ff ecting Quality
Number of bitsused for binaryencoding.Example: 4 bits
allow1
6amplitudevariations to berepresented.
9 8 7 6 7 9
Sampling Interval
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E ff ect of Sam pling F requency
Higher sampling frequency² Smaller sampling intervals
² Frequent sampling
² Better quality because the audio pattern iscaptured better
² Higher bandwidth required fortransmission
² Higher disk space required for storage
Computation of Bandwidth
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C om putation of BandwidthRequirement for Transmission
Problem:² Compute the audio streaming rate for a
voice grade circuit given that the number
of bits used in the sampling is 8 Background information
² A voice grade circuit has a bandwidth of
approximately 4000 Hz General rule
² For acceptable quality, the audio must besampled at twice the frequency of the voice
rade bandwidth
R f S li t T i th
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Reason for Sam pling at T wice theF requency
Two peaks in each cycle² Half of a cycle is above the datum line
² The other half of the cycle is below thedatum line
Therefore, sample the audio at twice the
frequency rate
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CD Sam pling?
Sampling in this case is done for higherquality
² 44 KHz
² 16-bits
² Stereo
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Pr oblem Representation
79 68 57 46 57 79
1/8000 Seconds (8000 HZ twice the frequency of the voicegrade circuit)or 2X4000 samples per second
8 bits are used enabling 256 amplitudes to
represent the humanvoice which is consideredto be adequate.
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Bandwidth C om putation for V oice
Number of samples² 8000 per second
Number of bits per sample² 8
Bandwidth requirement
² 8X8000 bps = 64,000 bps
² Approximately 64K bps
64K bps is the speed of a single ISDN
B channel desi ned to carr voice
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Bandwidth of V oice Circuits
Generally speaking, the bandwidthrequirement for uncompressed voice
circuit is 64 Kbps An example is the ISDN ² B channel
that was originally intended to carry
voice² Its bandwidth is 64 K bps
Examples in Audio Quality and
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Exam ples in Audio Quality and Bandwidth Requirement
CD quality² 44,100 Hz, 16 bit, Stereo
² 1376K bps Radio quality
² 22,050 Hz, 8 bit, mono
²1
76K bps Telephone quality² 11,025 Hz, 8bit, mono
² 88K bps
R di Q lit d B d idth
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Recor ding Quality and Bandwidth
Requirem
ent Dem
onstration
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Recor ding Used in this Exam ple
Settings for recording² 11K Hz, 8 bit and mono
Audio bandwidth requirement is 88Kbps
Streaming is required to send the audio
alone over the Internet Approximate bandwidth required for
both video and audio is 133K bps
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D li f I t ti O th
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Delivery of I nstr uction Over the
WWW
Client
WebSite
Receive audio/video usingInternet Explorer and MediaPlayer.
Audio/Video streaming.
Store streamed audio/video using Windows Media.
28-56K bps
Streaming Classroom Lectures on
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Streaming C lassr oom Lectures on CD
Bandwidth requirement as computedearlier is
Internet Ramp Bandwidth
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I nter net Ram p Bandwidth
C om
putation
WWW
A T1 line operating at approximately 1.354M bpscan support approximately 10 connections in theory.
In practice, 7 connections which is 70 percent of 10connections can be supported with due considerationgiven tobandwidth bottlenecks.
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Types of Multimedia Transmission
Unicasting
Multicasting
Broadcasting
Sampling Considerations In
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Sam pling C onsiderations I n
C omm
unications
Sender Receiver
Digital audio transmission
Adjust quality (sampling interval and bitrepresentation) to suit bandwidth availability.
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Audio F iles
Audio can be stored in different formats² Uncompressed or raw file format (wav)
² Compressed format
² Streaming formatStreamed audio is also compressed
It is also designed for real-time delivery ofaudio
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Audio F ile F or mat
wav file format² Basic file format in audio storage or raw file
rm file format
² Real audio·s streamed file format² Streamed file
wma file format² Microsoft·s audio streamed file format² Streamed file
mp3 file format² Compressed file
aac file format²
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End of Module
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Module
Quality Retention in Digital
Transmission
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Quality Retention
Quality is retained in digitaltransmission because only the codes are
transmitted Quality is subject to some deterioration
in analog transmission because the
wave pattern is transmitted
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Analog Audio Transmission
Audio Priorto Transmission
Audio withInterference
Transmission
Audio After Filtering
Passage of Analog Audio Over
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Passa ge of Analog Audio Over Analog Lines
AnalogAudio
Analog
Signals
AnalogSignals
AnalogAudio
Telephone
Telephone
Recreation of Audio from Analog
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Recreation of Audio f r om Analog
Si gnals A difficult task
Complex algorithms are used to filter
noise etc. for better audio transmission
Signal Passage in Digital Audio
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Si gnal Passa ge in Di gital Audio
Transm
issionEncode
TransmitRecreate
Decode
Audio
Audio
A Sample Digital Audio
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A Sam ple Di gital Audio
Transm
ission Path
AnalogAudio
DigitalAudio
DSL
Modem
DSLM
odem
DigitalAudioAnalogAudio
SoundCard
SoundCard
DigitalNetwork
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Sound Generation
Sound is recreated at destination² Using FM synthesis
² Using wave table generation Noise is not an issue in digital
communication although it is an issuein digital transmission² The reason, once again, is due to the fact
that only codes are transmitted in digitaltransmission
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Better Sound Generation
Wave table generation provides bettersound reproduction that FM synthesis
Digital Advantage in Audio
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Di gital Advanta ge in Audio Transmission
Only codes are transmitted
Original encoding is recreated
Original audio is reproduced
Again, sampling rate and number ofbits used in each sample will determine
the quality of audio transmitted
Digitized Signal Transmission
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Di gitized Si gnal Transmission Over Analog Lines
Encode
TransmitRecreate
Decode
Audio
Audio
Sampled Signals
Sample Digital Audio Transmission
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Sam ple Di gital Audio Transmission Path Over Analog Lines
AnalogAudio
DigitalAudio
Modem
Modem
DigitalAudioAnalogAudio
SoundCard
SoundCard
AnalogPSN
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Audio Transmission I n WWW
Client
WebSite
Receive audio usingInternet Explorerand Windows Media Player.
Audio stream over analog/digital line.
Real-time audiobroadcast supportusing Windows Mediastreaming server module.
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Analog to Di gital C onverter
A to D and D to A converter The chip that is responsible for this
conversion is known as the DSP (DigitalSignal Processor) chip
It is used in sound cards, modems etc.wherever there is a need for A to D and D toA conversion
The mass use of this chip in various deviceshas led to a drastic drop in the price of thechip and the devices
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Di gital Si gnal Pr ocessor (DSP )
DSP
DigitalAnalog
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End of Module
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Module
Digitization Of Image
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I ma ge Di gitization
Image can be of the form black andwhite, gray scales, color
Factors that influence the digitization ofimage are as follows
² Resolution measured in pixels
² Color depth expressed in number of colorvariations
Di gitization O f I ma ge:O i
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OverviewPixel
Horizontal Resolution
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Di gitization of the Letter L
Number of bits
determine theamount ofinformation thatcouldbe stored.
Digitization Of Image: The
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Di gitization O f I ma ge: ThePr ocess
Divide the image into a grid of pixelsthat may be considered as the sampling
points of the image Digitize information on each pixel
Store and transmit
R l ti
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Resolution
Horizontal resolution² Number of horizontal pixels
Vertical resolution² Number of vertical pixels
Image resolution
² Horizontal by vertical resolution² Ex: 640 by 480
Digitization of Black and White
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Di gitization of Black and WhiteI ma ge
White² A pixel lit represents a 1
Black² A pixel not lit represents a 0
Storage required per pixel² 1 bit
Storage required for 640 by 480resolution image² 640 times 480 bits = 307,200 bits = 38.4K
Bytes
Di gitization of I ma ge Using
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g f g gGray Scales
A pixel may take a value between 0 and15 for 16 gray scales
A gray scale of 3 can be coded as 0011 and the others similarly using this 4digit code
The bandwidth requirement for thetransmission of a 640X480 image in thiscase is as follows:
² 640X480X4 =1
53.5K Bytes
Di iti ti f C l I
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Di gitization of C olor I ma ge
Image coding² Each pixel may take a value between 0 and 255 if
256 colors are to be represented
Storage requirement² Digitizing of images requires substantial number
of bytes and hence large storage space forprocessing
Bandwidth requirement² Higher bandwidths are required to transmit color
images
Bandwidth C om putation for
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I ma ge with 256 C olors
Resolution is 640X480
8 bits are required to represent 256
colors bandwidth requirement for the
transmission of one image is as follows:
² 640X480X8 = 307.2K Bytes
The E ff ect of C olor Depth and
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ff f pResolution
Compare VGA, SVGA and XGA² XGA provides the highest resolution
Practical implication² More colors less resolution if bandwidth orstorage is the limiting concern
² Example 256 colors at lower resolution
16 colors at higher resolution Rule
² Higher the resolution the lower the number ofcolors available in general given the resourceconstraints such as bandwidth constraints
F actors A ff ecting Bandwidth
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Requirement in I ma ge Transmission
The higher the resolution, the higher thebandwidth requirement for transmission
The higher the color re
presentation, alsoknown as color depth, higher the bandwidth
requirement
For true color, 24 (32) bits are required torepresent each pixel
The file sizes in raw image capture can thusbecome very large
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End of Module
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Module
Compression of Digitized Images
Compression of Digitized Images
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C om pression of Di gitized I ma ges
Compression is required to reduce thesize of the image file
Large blocks of unchanged data in animage (background) offers anopportunity to compress the image
Image files are almost alwayscompressed
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A F ew C om pression F or mats
GIF
JPEG
MIC (Microsoft Image Composer)
PCD (KODAK) - Used by Corel
Uncompressed file exist in the form ofbit mapped file with the extension of.BMP
Image File Format Extensions
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I ma ge F ile F or mat Extensions
File formats often represent the compressionprocedure being used such as jpgrepresenting the jpeg compression technique
Examples:² Bmp ² uncompressed file format² Gif² jpg² pcd² tiff² pcx
Loss-less C om pression and
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Others
Some compression formats offer loss-free compression of the image
Others sacrifice minimal loss for thesake of reduced storage and bandwidthrequirements
Fortunately, the loss is not easilydetected by the naked eye
I ma ge Transmission
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C onsiderations
Sender Receiver
Adjust image to suit available bandwidth.
Adjustable features are as follows.- Resolution- Color depth
Adjusting the size also reduces the bandwidthrequirement because of a corresponding reductionin the number of pixels required to representthe image.
A Peek At Data Compression
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A Peek At Data C om pression
0 0 0 0 0 0 0 0 0 0 0 - - - - - -0 1 1 1 1 1 11 «... 0
THE ABOVE CAN BE COMPRESSEDINTO = #9000$0#
² 9000 bits are compressed into 8 characters
that require approximately 64 bits fortransmission
² 9000 ZEROS ARE CODED INTO #900$0#
#600$1#
INTERPRET WITHIN THE # SIGN
600
NUMBER COUNT1
CHARACTER BEINGTRANSMITTED
C i l
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C om pression Result
In the previous example, 9000 bits arecompressed into 8 characters
If 10 bits are used on the average fortransmitting each character, the 9000bits of information is now compressed
into 80 bits for transmission
Modem I m plication in I ma geT i i
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Transmission
Modems also compress the data stream toachieve higher transmission speeds
Because of the fact that the images are alreadycompressed, the full speed benefit may not berealized when images are transmitted over amodem connection
An already compressed image file does not,for instance, offer itself well to furthercompression in the modem
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End of Module
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Module
Digitization Of Video
Di iti ti f Vid
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Di gitization of V ideo
Digitization of video is an extension ofthe process of digitizing an image
It amounts to the transmission ofcertain number of still images known asframes per second
Obviously, digitized video requires
higher bandwidth for transmission andmore space for storage
Frame Rate
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F rame Rate
30 frames of images per second, in general,defines continuos motion
In communications, 25 frames per second isconsidered to be continuous motion
15 frames per second is currently used invideo conferencing over digital lines foracceptable reception of video
It is also possible to engage in videoconferencing at a frame rate of 5 frames persecond
C om putation of Bandwidth for R T i i f Vid
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Raw Transmission of V ideo
Image resolution is 640X480
Number of colors is 256 (8 bit)
Acceptable reception requires 15 framesper second
Therefore, the bandwidth for the raw
transmission is as follows:² 640X480X8X15 = 36.86M bps = 4.6M Bps
C om pression Standar ds Used in
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the Di gitization of V ideo
MPEG 1, MPEG 2, MPEG 3 and MPEG 4
WindowsMedia Video
Real Media Indio
QuickTime
ActiveMovie AVI
St i F t f Vid
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Streaming F or mats for V ideo
Various streaming formats aresupported by different vendors
² RealV
ideo Microsoft·s streaming format
² wma (WindowsMedia Audio)
² wmv (WindowsMedia Video)
² Active Streaming Format (ASF)
Apple·s QuickTime format
Etc.
Overview of V ideo Transmission
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in V ideo C onf erencing
Minimum speed² 3 to 5 frames per second
Acceptable speed² 15 frames per second
Transmission techniques
² Data is compressed² Only changes to the frame are transmitted
Bandwidth Optimization in
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V ideo C onf erencing
Minimize Windows for maximumefficiency
² Transmit less number of pixels inminimized form
Decrease the resolution² Has the same effect as above
Decrease the number of colorsdisplayed
C ommunication Links for V ideo
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C onf erencing
Possible on analog lines using 56,000bps transmission speed but not
desirable Digital lines are preferred and the
guidelines are as follows:
² Possible at1
28k bps using ISDN lines² Acceptable at 384k bps
² 1M bps and above offer good quality videotransmission
ISDN Li S it bilit
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I SDN Line Suitability
ISDN B channels can be assigned on adynamic basis depending on the
bandwidth requirement at any point intime during video conferencing
Vid C f i P d t
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V ideo C onf erencing Pr oducts
Intel ProShare
CU-See Me
Picturetel
C-phone
etc.
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End of Module