 to the session of CD and DVD player. Learning outcome of the session. Before proceeding, let me ask you one question. What is used before CD and DVDs are invented for video and audio recording? You can pause the video, think about the question, write down your answer in your notebook. You can resume the video to see the answer. Let me give you the answer. Before CDs and DVD players are invented, the video cassette recorders and cassette tape recorders are used. Compact disc player, popularly known as CD player. A CD player is the electronic device that plays compact disc. So, this is how the CD player looks. So, in this tray, we can insert the CD. So, what is a CD? A compact disc is popularly known as a CD. It is an optical storage medium with a digital data, which is recorded onto its surface. So, this is how the CD looks. So, this surface is used for the labeling of the CD and this is used for the recording purpose. So, this surface is a shiny so that the laser beam strike and reflect back to the photo detector. Later on we will see that and this is the dull surface. CD player reads the recorded data by means of the optical beam and accurately reproduces the original information which is stored. It may be music, picture or the data. Because the player reads the information by the optical means, there is no physical wear and tear of the disc. Compact disc. A compact disc is thin circular disc which is made of the metal and the plastic. It is about 12 centimeter in diameter. The diagram shows you the cross section of the compact disc. It is made up of the three layers. So, this is the protective layer which is made up of the polycarbonate. A middle layer is made up of the aluminum which is a reflective layer and this is the another plastic layer in order to protect the aluminum surface and this is the top layer which is covered with a lacquer. So, the most of the CDs are made up of the tough brittle plastic which is called as a polycarbonate. A middle layer is aluminum which is a reflective and on the top of the aluminum there is a protective layer of the plastic or the lacquer. It is shiny on the one side and dull on the other side. It is shiny on the one side so that the laser beam can reflect back the disc and read the information which is stored onto the disc and the dull side is generally used in order to provide the label of the CD. Let us see how the CDs are recorded and played back. Before CDs are invented the LP records and the cassette tapes are used for the recording of the music. The LP records the music as a grooves on the surface of the lacquer. As you can see from the animation the recorded sound is given to the stylus which has a sapphire tip. So, the stylus will vibrate as per the recorded sound. It reaches the grooves on the surface of the LP recording disc. By means of this the audio is recorded onto the surface of the disc. Whereas, in case of the cassettes the recording is done by using the magnetism. As you can see from the signal current will create the changing magnetic field and this changing magnetic field will magnetize the tape cassette tapes and by means of this magnetism the recording is done onto the cassette tapes. So these recordings are called as analog because the sounds are recorded as a continuous varying pattern in the form of the grooves or the fluctuating magnetic field onto the tape. But in case of the CDs the information is recorded by the digital means. The CDs are burled with the laser beam that itches the bumps called as a pits onto its surface. As you can see this is a microscopic view of the CD. So these are called as the pits which are burled by the laser beam. And the unburned area is called as a land. There is laser beam strike onto the reflective aluminum surface that burns the bump and create the pit. An unburned area is called as a land. So the bump represents the number zero. So every time the laser burns the bumps onto the surface the zero is stored onto the disc. The lack of the bump which is flat unburned area onto the disc called as a land that represents the number one. Thus a laser can store the all information sampled from the original track of the music by burning some areas to represent the zeroes and leaving some areas that is unburned to represent the one. Storage capacities of the CD. A CD can store up to the 74 minutes of the music. So the total amount of the digital data that can be stored onto the CD can be calculated as if you have 44,000 samples per channel per second which is multiplied by two bytes per sample because of the Nyquist criteria for sampling. And then there are two channels where hence we have to multiply it by two. Total minutes are 74 into the 60 seconds per minute. So we have total 780 megabytes that has to be stored onto the disc. On the size of the disc is about 12 centimeter only. CD player components as shown in a diagram there are basically three components. We have the disc motor then we have the laser system component and then a track assembly. So a driver motor spins the disc. The driver motor rotate in between 200 rpm to the 500 rpm depending on the which track is to be redid. A laser and the lens system focuses the laser beam onto the spiral and rid the bumps. The tracking mechanism moves the laser assembly so that the laser beam can follow the spiral track. Thus the tracking system has to be able to move the laser in the micron resolution. How the CD player works? The laser beam flashes onto the shiny side of the CD. The land reflect the laser light straight back while pits scatter the light. As you can see from the diagram the laser beam falls onto the pits and the land. So when this reflected light detected by the optical it will detect the logical one and when it is not reflected it will detect the logical zero. In this way the land represents the logic one and the pits represent the logic zero. And after that the digital data is given to the digital to analog converter that will convert this data into the analog and then it is amplified and given to the speaker. So the every time light reflect the back the photocell will detect it and realizes that it has seen the land and send the electrical signal to the electronic circuit that will generate the number one. So when the light fails to reflect back the photocell realizes that there is no land is available and hence doesn't register anything. So the electronic circuit generator will generate the number zero. A DVD player. A DVD player is very similar to the CD player with a laser assembly that shines the laser beam onto the surface of the disk to read the patterns of the bumps. This is a DVD player but the difference is that the DVD player uses the laser light that is high powered and has correspondingly finer focus point than that of the CD player. So this enables to have a shorter pits and narrower separation track so that the larger information can be stored onto the DVD than that of the CD. So DVD player components. As you can see that there are three main components. It has a drive motor, a laser and the lens assembly, a digital to analog converter and the digital signal processing system. A drive motor will spin the disk. The drive motor is precisely controlled, rotated in between 200 rpm to 500 rpm depending on which track is being readed. The laser and lens assembly focuses the laser beam onto the bumps and read them. The light from the laser has a smaller wavelength that is 614 nanometer than that of the light from the laser in the CD player. It has 718 nanometer which will allows the DVD player laser to focus onto the smaller DVD pits. A tracking mechanism that moves the laser assembly so that the laser beam can follow the spiral track. The tracking mechanism has to be able to move the laser at the micron resolution. Finally the data which is readed by the DVD player will be in the form of digital data that is 0 and 1 which is decoded by the digital to analog converter, further processed by the digital signal processor and then given to the amplifier and then played back. So what is a DVD? DVD stands for digital versatile disk. It provides 7 times larger storage capacity as compared to the CD. You can see this is the top side of the DVD and this is the bottom side of the DVD. A DVD is actually the two CDs which are glued together. A CD is read from and written by the one side only whereas the DVD can be read or written onto the both side depending on their manufacturer. This is the difference between the DVD and the CD. As you can see from the diagram this is a microscopic view of the CD and this is microscopic view of the DVD. The track distance is about in case of the DVD is about 0.74 micrometer whereas in case of the CD it is 1.6 micrometer. The length of the PIT is about 0.4 micrometer in case of the DVD. In case of the CD it is about 0.834 micrometer. The PIT width is about 0.3 micrometer in case of the DVD whereas in case of the CD it is about The depth of the pit is about 0.16 micrometer in case of the DVD, whereas in case of the CD the depth of the pit is about 0.11 micrometer, a laser wavelength if you compare it is about 635 to 650 nanometer in case of the DVD whereas in case of the CD it is about 780 to 790 nanometer. The speed of rotating speed in case of the DVD is about 3.49 meter per second whereas in case of the CD it is about 1.2 to 1.4 meter per second that is the scanning speed. The maximum user data rate bytes per second in case of the DVD will be 11.08 megabytes in case of the CD it is about 1.4 megabyte. So, the average user data rate in case of the DVD is about 4.7 Mbps in case of the CD it is about 3.7 Mbps. The capacity is obviously in case of the DVD is about range from 1.4 to 8 GB whereas in case of the CD it is about 642 maximum 700 Mbps. Let us see the double layered DVD disc. A DVD can be have two reflective metal layers that will allow the laser to read the data from both layers using the one side of the disc which will provide the double information capacity storage. So there are two heretics of the disc are available with the two metal layers for the information storage. The difference between these two is that these metal layers are connected together by the adhesive and this there is no adhesive is present in between the two layer. So how these two layers are formed? One of this layer is a semi reflective layer and another is a fully reflective layer. So you can see that this is a semi reflective layer. So the light can reflect back and again reflect and goes on to the second layer metal layer and this is not a semi reflective layer this is a fully reflective layer. So the light laser light strike on this layer and come back. These double layered DVDs provide up to the four time storage capacity as that of the single layered DVD. The outer layer is made up of silicon gold or silver alloy which is a semi reflective layer. So it will reflect back some of the laser beam and allow some of it to pass through the fully reflective layer that is made up of the aluminum. So it will reflect back the laser beam. So both parts thus reflected to and dictated by the photo sensor in the laser head which focuses on to the one layer at a time. These are the references for the session. Thank you.