Digitization of Audio.ppt

Chapter Overview of Analog and Digital Technologies

Chapter Objectives Explain the basic concepts of analog and digital technology Show the importance of frequency spectrum to communication along with an explanation of the concept of bandwidth Give an overview of the interface technology between analog and digital technology Describe the process of digitizing data, audio, image and video Discuss quality retention in digital transmission

Chapter Modules Overview of analog technology Frequency spectrum and bandwidth Digital technology Digital-to-Analog and Analog-to-Digital Interfaces Overview of Digitization of Information Digitization of Data Digitization of Audio Continued

Continuation of Chapter Modules Quality retention in digital transmission Digitization of image Digitization of video

MODULE Overview of Analog Technology

Areas of Application Old telephone networks Most television broadcasting at present Radio broadcasting

Analog Signals: The Basics Time Signal Frequency = Cycle/Second A typical sine wave Cycle Amplitude

Amplitude and Cylce Amplitude Distance above reference line Cycle One complete wave

Frequency Frequency Cycles per second Hertz is the unit used for expressing frequency Frequency spectrum Defines the bandwidth for different analog communication technologies

Information Representation Using Analog Signals Information can be represented using analog signals Analog signals cannot be manipulated easily Analog signals must be digitized for computer processing

Analog Digital Conversion 1 0 1 1 0 1 0 0 A to D Converters, Digital Signal Processors (DSP) etc.

Data Transmission Example Computer Modem Digital 0s and 1s Analog 0s and 1s Digital-to-Analog Modulation and vice versa

Voice Transmission Example Voice Carrier Wave AM Radio Transmission Analog-to-Analog Modulation

MODULE Frequency Spectrum and Bandwidth

Frequency Spectrum Defined Available range of frequencies for communication Starts from low frequency communication such as voice and progresses to high frequency communication such as satellite communication The spectrum spans the entire bandwidth of communicable frequencies

Frequency Spectrum Low Frequency High Frequency Radio Frequency Coaxial Cable MHz Satellite Transmission Microwave MHz Voice KHz

Frequency Spectrum Low-end Voice band Middle Microwave High-end Satellite communication

Bandwidth Definition Bandwidth, in general, represents a range of frequencies 300 MHz 700 MHz Bandwidth is 400 MHz

Usage of the Term Bandwidth To specify the communication capacity A medium such as a coaxial cable is associated with a bandwidth To indicate the bandwidth of a technology Voice grade circuits have a bandwidth of 4 KHz (0-4000 Hz)

Communication Capacity Bandwidth is indicative of the communication capacity Communication speed is proportional to bandwidth Shanon’s law Units used to represent bandwidth are MHz, Mbps etc.

Coaxial Cable Example Bandwidth of 300 MHz Comparison with twisted pair Higher bandwidth Supports faster communication speeds Supports multi-drop connection Coaxial Cable Multi-drop

Limiting Factors on Communication Speed Communication Speed Bandwidth Technology

Continuation of Bandwidth and Technology on Communication Speed Bandwidth limitation Use better technology such as data compression used in modems to increase speed of communication Bandwidth and technology limitation Move to higher bandwidth media such as fiber cables

Speed Dependency on Bandwidth and Technology Medium 1 example can be shielded twisted pair and medium 2 example can be fiber. Medium 1 Technology Medium 2 Higher Bandwidth

MODULE An Overview of Digital Technology

Areas of Application Computers New telephone networks Phased introduction into television broadcasting

Digital Technology Basis Digital signals that could be assigned digital values Digital computer technology Digital signals Binary representation Encoded into ones and zeros

Digital Advantage Processing using computer technology Programmable services Better quality due to being able to reconstruct exact digital patterns at the receiving end Faster communication speeds are possible

Digital Signal 1 0 1 1 0 1 0 0 Pulse Time Signal Strength Pulse Duration

Clock Speed and Pulse Duration Pulse Duration MHz

Clock Speed and Execution Speed Pulse duration is inversely proportional to the clock frequency Faster the clock speed, the smaller the pulse duration Smaller the pulse duration, the faster the execution in general

Clock Speed and Communication Speed Faster the clock speed, smaller the pulse duration Smaller the pulse duration, smaller the time taken to transmit one bit of information Therefore, faster the clock speed measured in MHz, faster the communication speed measured in Mbps in general

MODULE Digital-to-Analog and Analog-to-Digital Interfaces

The Need for Conversion Analog-to-Digital Connection of a computer to an analog communication line Digital-to-Digital Connection of a computer to a digital ISDN line

Digital-to-Analog Interface Comp. Sys. 1 Comp. Sys. 2 Modem Modem Digital Serial RS-232C Digital Serial RS-232C Analog ITU V.90 POTS

Digital-to-Digital InterfaceA Comp. Sys. 1 Comp. Sys. 2 ISDN Adapter ISDN Adapter Digital Serial RS-232C Digital Serial RS-232C Digital ISDN

MODULE Overview of Digitization Of Information

Module Objectives Define the representations of information Explain the need to digitize State the advantages of digitization

Digital Information Processing Data Audio Image Video Digitized and Encoded Digital Transmission

The Need to Digitize Essential for computer processing Essential for transmission Entry point to networks is a often a computer An increasing number of communication lines are digital lines

The Advantages of Digitization Information could be processed by the computer Easy transmission of information Minimize loss of quality during transmission

Codes Used in the Digitization Of Data Coding Standards ASCII EBCDIC Unicode ASCII Code example A=1000001

The Unicode Replace the ASCII coding system in microcomputers All variations of the Latin language English European languages Chinese and Japanese 18 Major languages Eg: Tamil

Unicode Possibilities It is a 16-bit code as opposed to the ASCII code that is basically an 8-bit code It is therefore possible to have 65,536 variations in UNICODE

Communication With ASCII And EBCDIC Latin languages can be transmitted in coded form Other languages Bit-mapped image transmission Requires considerably more bandwidth An exception is the use of true-type fonts to display the characters of a language not supported by ASCII

Communication With Unicode Binary encoded transmission Latin languages 18 major languages Chinese, Japanese etc. Transmission itself requires less bandwidth Universal usability of software in all the supported languages

Unicode Advantage in WWW Transmissions Client Tamil Web Site Internet Explorer Browser retrieving Tamil pages on a client supporting Unicode. Tamil pages are transmitted in their binary encoded form. Site created using all the tools such as the MS-IIS.

Transmission of Tamil Pages as Images on WWW Client Tamil Web Site Internet Explorer Browser retrieving Tamil pages similar to images. Binary image transmission of Tamil pages. Web pages scanned and stored as images.

Using Downloaded Fonts to Host and Transmit Tamil Pages Client Tamil Web Site Internet Explorer retrieving Tamil pages. Site created with tools such as MS-IIS. Download and install the Tamil fonts. Binary encoded form. Bandwidth requirements are low.

Digitization Of Audio: Overview Take samples of audio at pre-determined time intervals known as the sampling rate Represent the sampled audio with digital signals Pulse Amplitude Modulation (PAM) Encode signals into binary code Pulse Code Modulation (PCM) that incorporates PAM as well Required for computer processing

Digitization of Audio: Pulse Amplitude Modulation (PAM) Audio 9 8 7 6 7 9 Digital Signals must further be encoded into binary signals for computer processing and transmission. Sampling Interval

Digitization and Encoding of Audio: Pulse Code Modulation (PCM) PCM is a two step process First the audio is sampled and represented by digital signals The digital signals are then encoded in binary form

Binary Encoding of Signals in Pulse Code Modulation (PCM) 9 8 7 6 5 6 1001 1000 0111 0110 0101 0110 The integer numbers have effectively been coded into zeros and ones. The ones and zeros now contain the audio information encoded in a form that could be processed by a computer. PCM

Salient Points on the Digitization Of Audio Sampling rate and the number of bits used 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 original quality by extracting the pattern from the digital code

Effect of Sampling Frequency Higher sampling frequency Smaller sampling intervals Frequent sampling Better quality because the audio pattern is captured better Higher bandwidth required for transmission Higher disk space required for storage

MODULE Audio Quality Vs Bandwidth in Audio Transmission

Module Objectives Discuss the two important factors that influence the quality of digitized audio Outline the procedure for computing bandwidth requirement based on the factors mentioned above Present bandwidth requirements for sample audio formats Introduce the concept of audio streaming on the WWW

Factors Affecting Quality Number of bits used for binary encoding. Example: 4 bits allow 16 amplitude variations to be represented. 9 8 7 6 7 9 Sampling Interval

Computation of Bandwidth Requirement for Transmission Problem: Compute the audio streaming rate for a voice grade circuit given that the number of bits used in the sampling is 8 Background information A voice grade circuit has a bandwidth of approximately 4000 Hz General rule For acceptable quality, the audio must be sampled at twice the frequency of the voice grade bandwidth

Problem Representation 79 68 57 46 57 79 1/8000 Seconds or 2X4000 samples per second 8 bits are used enabling 256 amplitudes to represent the human voice which is considered to be adequate.

Bandwidth Computation Number of samples 8000 per second Number of bits per sample 8 Bandwidth requirement 8X8000 bps = 64,000 bps Approximately 64K bps 64K bps is the speed of a single ISDN (B) channel

Examples in Audio Quality and Bandwidth Requirement CD quality 44,100 Hz, 16 bit, Stereo 1376K bps Radio quality 22,050 Hz, 8 bit, mono 176K bps Telephone quality 11,025 hz, 8bit, mono 88K bps

Recording Quality and Bandwidth Requirement Demonstration

Recording Used in this Example Settings for recording 11K Hz, 8 bit and mono Audio bandwidth requirement is 88K bps Streaming is required to send the audio alone over the Internet Approximate bandwidth required for both video and audio is 133K bps

Audio Transmission In WWW Client Receive audio using Internet Explorer and a plug-in to receive the audio stream. Audio streaming requires compression. Real-time audio broadcast support using streaming server module. 28-56K bps Web Site

Delivery of Instruction Over the WWW Client Web Site Receive audio/video using Internet Explorer. Audio/Video streaming. Store streamed audio/ video using StreamCam. 28-56K bps

Internet Ramp Bandwidth Computation WWW A T1 line operating at approximately 1.354M bps can support approximately 47 connections in theory. In practice, 23 connections which is half of 47 can be supported with due consideration given to bandwidth bottlenecks.

Sampling Considerations In Communications Sender Receiver Digital audio transmission Adjust quality (sampling interval and bit representation) to suit bandwidth availability.

MODULE Quality Retention In Digital Transmission

Module Objectives The overall purpose is to discuss the retention of audio quality under digital transmission by comparing the same under analog transmission Discuss briefly the transmission of audio over the WWW Provide a brief introduction to the role played by the Digital Signal Process or DSP in digitizing audio

Analog Audio Transmission Audio Prior to Transmission Audio with Interference Transmission Audio After Filtering

Passage of Analog Audio Over Analog Lines Analog Audio Analog Signals Analog Signals Analog Audio Telephone Telephone

Recreation of Audio from Analog Signals A difficult task Complex algorithms are used to filter noise etc. for better audio transmission

Signal Passage in Digital Audio Transmission Encode Transmit Recreate Decode Audio Audio

A Sample Digital Audio Transmission Path Analog Audio Digital Audio ISDN Adapter ISDN Adapter Digital Audio Analog Audio Sound Card Sound Card ISDN Lines

Sound Generation Sound is recreated at destination Using FM synthesis Using wave table generation Noise is not an issue in digital transmission

Digital Advantage in Audio Transmission Only codes are transmitted Original encoding is recreated Original audio is reproduced Again, sampling rate and number of bits used in each sample determine the quality

Digitized Signal Passage Over Analog Lines Encode Transmit Recreate Decode Audio Audio Limited Sampling

A Sample Digital Audio Transmission Path Analog Audio Digital Audio Modem Modem Digital Audio Analog Audio Sound Card Sound Card Analog PSN

Audio Transmission In WWW Client Web Site Receive audio using Internet Explorer and RealAudio plug-in. Audio stream over analog/digital line. Real-time audio broadcast support using RealAudio streaming server module.

Digital Signal Processor DSP Digital Analog

Module Objectives Give an overview of the process of digitizing an image Black and white, gray scales, color Compute sample storage and bandwidth requirement for images with the following characteristics Black and white, 16 gray scales and color Discuss the factors influencing bandwidth requirement in image transmission

Digitization Of Image: Overview Pixel Horizontal Resolution Vertical Resolution

Digitization of the Letter L Number of bits determine the amount of information that could be stored.

Digitization Of Image: The Process Divide the image into a grid of pixels that may be considered as the sampling points of the image Digitize information on each pixel Store and transmit

Resolution Horizontal resolution Number of horizontal pixels Vertical resolution Number of vertical pixels Image resolution Horizontal by vertical resolution Ex: 640 by 480

Digitization of Black and White Image White A pixel lit represents a 1 Black A pixel not lit represents a 0 Storage required per pixel 1 bit Storage required for 640 by 480 resolution image 640 times 480 bits = 307,200 bits = 38.4K Bytes

Digitization of Image Using Gray Scales A pixel may take a value between 0 and 15 for 16 gray scales A gray scale of 3 can be coded as 0011 and the others similarly using this 4 digit code The bandwidth requirement for the transmission of a 640X480 image in this case is as follows: 640X480X4 = 153.5K Bytes

Digitization of Color Image Image coding Each pixel may take a value between o and 255 if 256 colors are to be represented Storage requirement Digitizing of images requires substantial number of bytes and hence large storage space for processing Bandwidth requirement Higher bandwidths are required to transmit color images

Bandwidth Computation for Image with 256 Colors Resolution is 640X480 8 bits are required to represent 256 colors bandwidth requirement for the transmission of one image is as follows: 640X480X8 = 307.2K Bytes

The Effect of Color Depth and Resolution Compare VGA and SVGA SVGA provides higher resolution Practical implication More colors less resolution 256 colors at lower resolution 16 colors at higher resolution Rule Higher the resolution the lower the number of colors available

Factors Affecting Bandwidth Requirement in Image Transmission The higher the resolution, the higher the bandwidth required The higher the color representation, also known as color depth, higher the bandwidth requirement For true color, 24 bits are required to represent each pixel The file sizes in raw image capture can thus become very large

MODULE Compression of Digitized Images

Module Objectives Briefly outline the factors conducive to the compression of images List a few image compression formats Explain image compression using a simple example Discussion the implication of transferring image files over a modem connection

Compression of Digitized Images Compression is required to reduce the size of the image file Large blocks of unchanged data in an image (background) offers an opportunity to compress the image Image files are almost always compressed

A Few Compression Formats GIF JPEG MIC (Microsoft Image Composer) PCD (KODAK) - Used by Corel

Image File Format Extensions File formats often represent the compression procedure being used Examples: tiff pcd gif pcx bmp

Loss-less Compression and Others Some compression formats offer loss-free compression of the image Others sacrifice minimal loss for the sake of reduced storage and bandwidth requirements Fortunately, the loss is not easily detected by the naked eye

Image Transmission Considerations Sender Receiver Adjust image to suit available bandwidth. Adjustable features are as follows. - Resolution - Color depth Adjusting the size also reduces the bandwidth requirement because of a corresponding reduction in the number of pixels required to represent the image.

A Peek At Data Compression 0 0 0 0 0 0 0 0 0 0 0 - - - - - -0 1 1 1 1 1 11 …... 0 THE ABOVE CAN BE COMPRESSED INTO = #9000$0# 9000 bits are compressed into 8 characters that require approximately 64 bits for transmission 9000 ZEROS ARE CODED INTO #900$0# #600$1# INTERPRET WITHIN THE # SIGN 600 NUMBER COUNT 1 CHARACTER BEING TRANSMITTED

Modem Implication in Image Transmission Modems also compress the data stream to achieve higher transmission speeds Because of the fact that the images are already compressed, the full speed benefit may not be realized when images are transmitted over a modem connection An already compressed image file does not, for instance, offer itself well to further compression in the modem

Module Objectives Present the digitization of video as an extension of the digitization of image Give an overview of video transmission in video conferencing Discuss the various analog and digital lines that could be used for video conferencing List a few commercially available video conferencing products

Digitization Of Video Digitization of video is an extension of the process of digitizing image 30 frames of images per second, in general, defines continuos motion In communications, 25 frames per second is considered to be continuous motion 15 frames per second is currently used in video conferencing over digital lines for acceptable reception of video

Computation of Bandwidth for Raw Transmission of Video Image resolution is 640X480 Number of colors is 256 (8 bit) Acceptable reception requires 15 frames per second Therefore, the bandwidth for the raw transmission is as follows: 640X480X8X15 = 36.86M bps = 4.6M Bps

Compression Standards Used in the Digitization of Video MPEG 1 and MPEG 2 Indio Video for Windows QuickTime ActiveMovie AVI

Streaming Formats for Video Various streaming formats are supported by different vendors RealVideo Microsoft’s streaming format Active Streaming Format (ASF)

Overview of Video Transmission in Video Conferencing Acceptable speed 15 frames per second Transmission techniques Data compression Only changes to the frame are transmitted

The Effect of Size of Window on Video Conferencing Minimize for maximum efficiency Transmit less number of pixels in minimized form

Communication Links for Video Conferencing Possible on analog lines using 28,800 bps transmission speed but not desirable Digital lines are preferred and the guidelines are as follows: Possible at 128k bps using ISDN lines Acceptable at 384k bps 1M bps and above offer good quality video transmission

Video Conferencing Products Intel ProShare CU-See Me Picturetel C-phone etc.

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