Output Devices

OUT PUT DEVICES DEALING WITH VIDEO & SOUND Until 1960s, the computers were unaware of display screens and sound systems they were a little more than a gigantic calculators controlled by switches dials and buttons. But today, modern display and sound systems make the computing more sophisticated. Because of modern output technologies computers are easier to use, data is easier to manage and information is easier to access. This includes monitor displays and sound system and how they work.

Contents • • • • • • • • • • •

Hardware Input Devices & Output Devices Visual Output Devices Monitors Ergonomics Graphic cards Projectors Sound Systems Sound cards Sub woofers Headphone

1- HARD WARE Hardware is a part that we can touch. Hardware includes input devices, output devices, processing devices and storage devices. A computer is a system that collects, processes, outputs, and stores information.

Input Devices Input devices are necessary to provide ways to communicate with the computer. Information and commands are issued to the computer by way of these devices. Examples of input devices include the keyboard, mouse, modem, joystick, digitizing pen and tablet, microphone, touch screens, scanner, camera.

How They Work? The main circuit board of a computer is called the motherboard. The main chip in the computer is the central processing unit CPU. It is called the CPU because its main function is to process instructions, manage the flow of information through the computer system, and perform calculations. It is the heart of the computer and communicates with the output, input and storage devices to perform tasks that are important to the functioning of the computer

Output devices In order to communicate with the computer and get the results of the information you have put into the computer, output devices are needed. Outputted information can be displayed as screen information, printed on paper, or outputted as sound. Examples of output devices include speakers, monitor, printers, and I/O Architecture

How They Work? Output is the result of processes that are done on the computer. An output device receives information from the computer and translates it from machine language to a form that humans can read or so that another machine can read the information. Types of Output Devices Output that is readable by the user can be categorized into two categories: Hard copy Hard copy is a relatively permanent form of output that can be read immediately or stored for later use, such as paper. Printers are the most common hard copy output devices. Soft copy Soft copy is a transient form of output, for example, text on a screen display. It is lost when the computer is turned off unless it is saved in the main memory or on a disk.

VISUAL OUTPUT DEVICES Monitors Display devices are the visual output devices of computers, the most common type being a monitor. A monitor looks like a television and has a screen. The monitor will display what the user is doing so he or she can see it before producing a hard copy. •

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A color monitor can display text or graphics in colour. Colour monitors are used very widely today. Some are capable of displaying millions of colours, more than the human eye can see, but the average monitor will display up to 256 colours at one time. Monochrome monitors display a single colour such as green or amber on a black background or black characters on a white background. These monitors are less expensive than colour ones and are often used for word processing.

Types Of Monitors CRT Monitors LCD Monitors CRT MONITORS The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to form images in the form of light emitted from the fluorescent screen. The image may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets and others. The single electron beam can be processed in such a way as to display moving pictures in natural colors. The CRT uses an evacuated glass envelope which is large, deep, heavy, and relatively fragile.

Working of CRT The cathode rays are now known to be a beam of electrons emitted from a heated cathode inside a vacuum tube and accelerated by a potential difference between this cathode and an anode. The screen is covered with a phosphorescent coating (often transition metals or rare earth elements), which emits visible light when excited by high-energy electrons. The beam is deflected either by a magnetic or an electric field to move the bright dot to the required position on the screen.

In television sets and computer monitors the entire front area of the tube is scanned systematically in a fixed pattern called a raster. An image is produced by modulating the intensity of the electron beam with a received video signal (or another signal derived from it). In all CRT TV receivers except some very early models, the beam is deflected by magnetic deflection, a varying magnetic field generated by coils (the magnetic yoke), driven by electronic circuits, around the neck of the tube.

Electron gun The source of the electron beam is the electron gun, which produces a stream of electrons through thermionic emission, and focuses it into a thin beam. The gun is located in the narrow, cylindrical neck at the extreme rear of a CRT and has electrical connecting pins, usually arranged in a circular configuration, extending from its end. These pins provide external connections to the cathode, to various grid elements in the gun used to focus and modulate the beam, and, in electrostatic deflection CRTs, to the deflection plates. Since the CRT is a hot-cathode device, these pins also provide connections to one or more filament heaters within the electron gun. When a CRT is operating, the heaters can often be seen glowing orange through the glass walls of the CRT neck. The need for these heaters to 'warm up' causes a delay between the time that a CRT is first turned on, and the time that a display becomes visible. In older tubes, this could take fifteen seconds or more; modern CRT displays have fast-starting circuits which produce an image within about two seconds, using either briefly increased heater current or elevated cathode voltage. Once the CRT has warmed up, the heaters stay on continuously. The electrodes are often covered with a black layer, a patented process used by all major CRT manufacturers to improve electron density. The electron gun accelerates not only electrons but also ions present in the imperfect vacuum (some of which result from outgassing of the internal tube components). The ions, being much heavier than electrons, are deflected much less by the magnetic or electrostatic fields used to position the electron beam. Ions striking the screen damage it; to prevent this the electron gun can be positioned slightly off the axis of the tube so that the ions strike the side of the CRT instead of the screen. Permanent magnets (the ion trap) deflect the lighter electrons so that they strike the screen. Some very old TV sets without an ion trap show browning of the center of the screen, known as ion burn. The aluminium coating used in later CRTs reduced the need for an ion trap. When electrons strike the poorly-conductive phosphor layer on the glass CRT, it becomes electrically charged, and tends to repel electrons, reducing brightness (this effect is known as "sticking"). To prevent this the interior side of the phosphor layer can be covered with a layer of aluminium connected to the conductive layer inside the tube, which disposes of this charge. It has the additional advantages of increasing brightness by reflecting towards the viewer light emitted towards the back of the tube, and protecting the phosphor from ion bombardment.

MODELS OF CRT MONITORS HP-775MF CRT monitor 775EA CRT monitor CRT Monitor MT1773 15 inch normal flat crt monitor

LCD Monitors liquid crystal display (LCD) is an electro-optical amplitude modulator realized as a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is often utilized in battery-powered electronic devices because it uses very small amounts of electric power Working of LCD It consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are (in most of the cases) perpendicular to each other When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field, distorting the helical structure (this is resisted by elastic forces since the molecules are constrained at the surfaces). This reduces the rotation of the polarization of the incident light, and the device appears grey. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray. LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are parallel.

The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). These devices can also be operated between parallel polarizers, in which case the bright and dark states are reversed. The voltage-off dark state in this configuration appears blotchy, however, because of small variations of thickness across the device. Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field). When a large number of pixels are needed in a display, it is not technically possible to drive each directly since then each pixel would require independent electrodes. Instead, the display is multiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together (typically in columns), and each group gets its own voltage source. On the other side, the electrodes are also grouped (typically in rows), with each group getting a voltage sink. The groups are designed so each pixel has a unique, unshared combination of source and sink. The electronics, or the software driving the electronics then turns on sinks in sequence, and drives sources for the pixels of each sink. Models of LCD Stereoscopic (3D) LCD Monitors Plasma Display Panel (PDP) Touch Screen Monitors Open-Frame LCD Monitors Interactive whiteboard (IWB) Multi-screen LCD monitors

Monitors features Compatibility: First demand for any monitor is compatibility with the other parts of the computer system. Input signal to the monitor must be compatible with output signal from the PC. Check out the documentation for the video card on your PC to make sure that it will be able to support the resolution and refresh rate of the monitor you select. Digital/Analog Input: All CRT monitors use a standard analog input from the PC. LCD or flat panel monitors use a Digital Flat Panel (DFP) port. These inputs improve image quality and reduce the price of the monitor. But, these inputs require that the monitor is used with a PC from the same manufacturer that also has a DFP output. Monitors size: Monitors come in different sizes. Usually you can buy 15,17,19, 21 , 23-inch and more sizes of the monitors. The VIS(Viewable Image Size) is the area that will be your available workspace — generally about an inch smaller than the screen size. The large size monitors (17 inches or more) cost more money and use more energy than smaller ones. But you will get additional workspace, more control over image resolution and appearance, and less strain on your eyes. If you look at extensive on-screen documents and spreadsheets, if you design your own web site, or even if you just play many of the newer computer games, a largescreen monitor is the best choice for you. Resolution: A monitors resolution is measured in number of pixels used to create the image. Most monitors have a resolution of 800 x 600 pixels up to 1280 x 1024 pixels. The first digit is the number of pixels that can be displayed horizontally on the screen, and the second digit how many can be displayed vertically. The higher the resolution, the more pixels that can be displayed. The more pixels, the crisper the image will appear. Refresh rate: To avoid a "flickering effect on your screen, you will want to check for a high refresh rate — the number of times per second the image is redrawn on the screen. A refresh rate of 75Hz or higher, is essential for standard monitors. LCD monitors have a fixed resolution, so refresh rate is less important. Dot pitch is the spacing between the colored dots that form the image on the screen. The smaller the dot pitch, the sharper the image. Look for a dot pitch of . 28mm or less to ensure a clear, sharp picture. Aspect ratio: The aspect ratio of the image is the ratio of the number of horizontal pixels to the number of vertical pixels. The standard aspect ratio for PCs is 4:3, but some resolutions use a ratio of 5:4. Anti-glare coating makes it easier to look at the screen under a bright light. Lastly, the shadow mask can make a difference in picture quality. Energy Star Compliant: Energy Star is a voluntary rating system established by the U.S. Department of Energy, the U.S. Environmental Protection Agency and

electronics manufacturers. Energy Star labeled products usually surpass Federal energy efficiency standards by 20% or more. MPR Compliant, Blue Angel Compliant, etc. The term MPR compliant for CRT monitors refers to a Swedish standard for electromagnetic radiation. This monitor radiation can be from low-frequency magnetic fields, electric fields, x-ray radiation, and static electric fields. This standard is quite comprehensive and various measurements are made at different points on the monitor for all of the mentioned types of radiation. These are given certain acceptable limits and it is a good assurance that the monitor is as safe as possible. Most monitors now comply with this standard. "Blue Angel Compliant" means to meet the German's requirements for lower power consumption and environmental specifications. It guarantees employers an easy compliance to the latest European social directives on Visual Display Units (VDU). Screen Controls: Many monitors have on-screen controls (ONC), enabling you to see the adjustments you're making to monitor as you make them, on screen. Ergonomic Monitor: Ergonomics is a science concerned with designing safe and comfortable machines for humans Positioning your Ergonomic Monitor to a Perfect height and distance that is comfortable for you with an Ergonomic Monitor arm or lift mechanism. Most of your time is spent looking at the Ergonomics Monitor. Hence, utmost care should be given in choosing and appropriately placing it in your workstation.

Graphics Cards The images you see on your monitor are made of tiny dots called pixels. At most common resolution settings, a screen displays over a million pixels, and the computer has to decide what to do with every one in order to create an image. To do this, it needs a translator -- something to take binary data from the CPU and turn it into a picture you can see. Unless a computer has graphics capability built into the motherboard, that translation takes place on the graphics card. A graphics card's job is complex, but its principles and components are easy to understand. In this article, we will look at the basic parts of a video card and what they

do. We'll also examine the factors that work together to make a fast, efficient graphics card.

The graphics card creates a wire frame image, then fills it in and adds textures and shading. Think of a computer as a company with its own art department. When people in the company want a piece of artwork, they send a request to the art department. The art department decides how to create the image and then puts it on paper. The end result is that someone's idea becomes an actual, viewable picture. A graphics card works along the same principles. The CPU, working in conjunction with software applications, sends information about the image to the graphics card. The graphics card decides how to use the pixels on the screen to create the image. It then sends that information to the monitor through a cable. Creating an image out of binary data is a demanding process. To make a 3-D image, the graphics card first creates a wire frame out of straight lines. Then, it rasterizes the image (fills in the remaining pixels). It also adds lighting, texture and color. For fast-paced games, the computer has to go through this process about sixty times per second. Without a graphics card to perform the necessary calculations, the workload would be too much for the computer to handle. The graphics card accomplishes this task using four main components: • • • •

A motherboard connection for data and power A processor to decide what to do with each pixel on the screen Memory to hold information about each pixel and to temporarily store completed pictures A monitor connection so you can see the final result

A video card, also known as a graphics accelerator card, display adapter, or graphics card, is a hardware component whose function is to generate and output images to a display. It operates on similar principles as a sound card or other peripheral devices. The term is usually used to refer to a separate, dedicated expansion card that is plugged into a slot on the computer's motherboard, as opposed to a graphics controller integrated

into the motherboard chipset. An integrated graphics controller may be referred to as an "integrated graphics processor" (IGP). Some video cards offer added functions, such as video capture, TV tuner adapter, MPEG2 and MPEG-4 decoding or even FireWire, mouse, light pen, joystick connectors, or even the ability to connect multiple monitors. A common misconception regarding video cards is that they are strictly used for Video games; a misconception that companies take advantage of in order to sell their products by advertising their products as if they were in fact video consoles. Video cards instead have a much broader range of capability. Being specialized for video output Video Cards improve what a computer monitor displays. As well, they play a very important role for Graphic Designers and 3D Animators, who tend to require optimum displays for their work as well as faster rendering in order to efficiently tone up their work. Video cards are not used exclusively in IBM type PCs; they have been used in devices such as Commodore Amiga (connected by the slots Zorro II and Zorro III), Apple II, Apple Macintosh, Atari Mega ST/TT (attached to the MegaBus or VME interface), Spectravideo SVI-328, MSX, and in video game consoles

PROJECTORS The Data projector is a device that takes a signal from a computer or video and projects an image on to a screen or a wall. The data projector is a device that takes a signal from a computer or video and projects the image onto a screen or a wall. They are commonly used for doing presentations or lectures to large groups of people using a pre prepared presentation. These presentations are often done with a piece of software called Power Point which is designed for making slide show like presentations. Data projectors can only project data from a computer or a video if you need to project other formats such as 35mm slides or overhead transparency's you will need to translate them into another format compatible with a computer or video or use a 35 mm slide or overhead projector instead. The data projectors are compatible with most computers. All the data projector does is act like a monitor. You can use PC's, Apple Macs, and various types of unix clone. I have only come across one computer that wouldn't connect to the projector in a usable way. It was a laptop of the same model that was used by noah to check off the animals as they entered the ark. There was a problem with the video card so you only got half the picture.

This however is unlikely to occur ever again as manufacturers have standards to adhere to now and it is in their interest to do so.

Operation with desktop computers in setting up projectors In order for the projector to work it needs a surface onto which it can project an image. The walls of rooms are normally quite adequate for this purpose. The surface should be even and a pale colour, preferably white. If the walls are an odd colour or are not very even a screen will be required. These can be requested from the AV dept. Please think as to whether you really need one before booking as there are not that many available and also they will increase the amount of time required for the set up. The projector needs to be positioned somewhere between 3 to 4 metres away from the surface in order that there is not too much loss of the light output. The projector will then need to be connected to the computer. How this is done will vary a little bit depending on whether you are using a desktop computer with a separate monitor or a laptop with an integral lcd screen. Connection to a Desktop Computer Stuff required: Computer, Projector, 1x Male to Male VGA lead, 1 x Male to Female VGA lead, Mains extension leads to suit the needs of the room.

The desk top computer has many connectors on the back of it the projector will need to be connected to the socket that the monitor is normally connected to. This will look similar to this example here. The colours may be different but the shape and the pin layout of the socket will remain the same. The other useful feature is that mostly there will only be one of these sockets on the computer. The very good news is that there will only be one socket that fits the plug on the lead provided for the connection of the computer and the projector (VGA Male to Male). This lead will need to be run between the output of the computer to the socket on the projector labelled VGA in. Another lead will need to be run from the projector, from the socket labelled "monitor out" to the monitor. This will be the VGA Male to Female lead as the monitor has a male plug on the end of the lead attached to it. Then the mains leads can be connected to the projector and the computer and they can be turned on. The projector should at this point be showing a blue light on the screen or wall. It may have some writing on it. This will vary from projector to projector. When the computer has finished booting you should be able to see the image of your desktop environment on the screen & the monitor. The projector will need to be focussed onto the surface by using either the control buttons on the projector or the focus ring on the lens depending on what model of projector you have. The size of the screen can also be adjusted using either the zoom buttons on the projector or the other lens ring. Again this is dependent on

the model of the projector you are using. Operations with desktop in settingup with laptops In order for the projector to work it needs a surface onto which it can project an image. The walls of rooms are normally quite adequate for this purpose. The surface should be even and a pale colour, preferably white. If the walls are an odd colour or are not very even a screen will be required. These can be requested from the AV dept. Please think as to whether you really need one before booking as there are not that many available and also they will increase the amount of time required for the set up. The projector needs to be positioned somewhere between 3 to 4 meters away from the surface in order that there is not too much loss of the light output. The projector will then need to be connected to the computer. How this is done will vary a little bit depending on whether you are using a desktop computer with a separate monitor or a laptop with an integral lcd screen. Connection to a Laptop Computer Stuff required: computer, Projector, 1 x Male to Male VGA lead, Mains extensions to suit the needs of the room. The male to male VGA lead needs to be connected between the laptop and the data projector. At the laptop end there will only be one socket that the lead fits into (a high density 15 pin D sub connector) The lead needs to be carefully fitted into the socket. Please make sure you have the plug the right way up and if it doesn't fit easily don't force it in. There will be a reason why it won't fit. Is it the right way round? The other end of the lead needs to be connected to the data projector in the socket labelled computer in. The set up of the laptop computer differs from the set-up of a desktop computer here because the laptop does not require a return lead from the projector to the monitor. This is because, as you may by now have noticed, the screen on a laptop is integral to the machine. Once this cable is connected boot up the computer and turn on the projector ( did I mention you may need to plug it in to the mains electricity supply? No? Oh well you know now.) The projector will need to be focussed onto the projection surface using either the buttons on it or the lens ring (this is dependent on the model used). At this stage you may not have a picture on the screen. This is not yet a cause for panic. The laptop has a feature that the desktop computer doesn't have. You can control where the video signal is sent. You can have either one of three states. 1. The projector display only. 2. The laptop display only or 3. both displays at the same time. Switching between these states using the keyboard, varies from machine to machine but all will be labelled in a similar way. The example I have provided uses the FN & F8 key combination. Each time this combination of keys is pressed the computer will take one step through the three step cycle. Other machines may use the FN & F5 or another combination. All of the machines will be labelled on the keyboard somewhere, either with text or a logo of a monitor. The other consideration that needs to be taken into account when using laptops for presentations is the power management settings. The laptop will behave differently in terms of going to sleep when there is no mains power available for it. It will probably be set to conserve its battery jealously and to go to sleep at the first sign of inattention by its user. This can be quite bad if you have just been talking for a while without changing

your display slide. There is nothing worse than doing a presentation for hundreds of people and even your computer can't stay awake. Please check your power management settings before your presentation. screen resolution adjustment The projectors as with monitors can only deal with certain screen resolutions. Some of them are fine with very large screen sizes and some can not cope with video signals in this range. The newer projectors can cope with resolutions of 1280 x 1024 and lower. Some of the older models can only cope with 800 x 600 and lower. This means that you may have to adjust the video signal output of your computer to levels that the projector & your computer can deal with. The chances are that if your computer is fairly new it will be able to do 1024 x 768 without any problems, newer ones up to 1280 x 1024. This limitation is due to the speed and memory available on the video card. This is the part inside your computer that transfers the digital information into an analogue signal for the monitor to display.

SOUND SYSTEMS Speakers and their associated technologies are key sound output systems. PC audio systems includes premium sound cards and tweeters, mid range speakers and sub range woofers for sound quality that rivals home stereo systems SOUND CARD Sound is a relatively new capability for PCs because no-one really considered it when the PC was first designed. The original IBM-compatible PC was designed as a business tool, not as a multimedia machine, so it's hardly surprising that nobody thought of including a dedicated sound chip in its architecture. Computers, after all, were seen as calculating machines; the only kind of sound necessary was the beep that served as a warning signal. For years, the Apple Macintosh had built-in sound capabilities far beyond the realms of the early PC's beeps and clicks, and PCs with integrated sound are a recent phenomenon. By the second half of the 1990s PCs had the processing power and storage capacity for them to be able to handle demanding multimedia applications. The sound card too underwent a significant acceleration in development in the late 1990s, fuelled by the introduction of AGP and the establishment of PCI-based sound cards. Greater competition between sound card manufacturers - together with the trend towards integrated sound - has led to ever lower prices. However, as the horizons for what can be done on a PC get higher and higher, there remain many who require top-quality sound. The result is that today's add-in sound cards don't only make games and multimedia applications sound great, but with the right software allow users to compose, edit and mix their own music, learn to play the instrument of their choice and record, edit and play digital audio from a variety of sources.

Other Sound Card Components In addition to the basic components needed for sound processing, many sound cards include additional hardware or input/output connections, including: •

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Digital Signal Processor (DSP): Like a graphics processing unit (GPU), a DSP is a specialized microprocessor. It takes some of the workload off of the computer's CPU by performing calculations for analog and digital conversion. DSPs can process multiple sounds, or channels, simultaneously. Sound cards that do not have their own DSP use the CPU for processing. Memory: As with a graphics card, a sound card can use its own memory to provide faster data processing. Input and Output Connections: Most sound cards have, at the very minimum, connections for a microphone and speakers. Some include so many input and output connections that they have a breakout box, which often mounts in one of the drive bays, to house them. These connections include: o Multiple speaker connections for 3-D and surround sound o Sony/Philips Digital Interface (S/PDIF), a file transfer protocol for audio data. It uses either coaxial or optical connections for input to and output from the sound card. o Musical Instrument Digital Interface (MIDI), used to connect synthesizers or other electronic instruments to their computers. o FireWire and USB connections, which connect digital audio or video recorders to the sound card

Other Options for Sound Control Not every computer has a sound card. Some motherboards feature integrated audio support instead. A motherboard that has its own DSP can process multiple data streams. It may also support 3-D positional and Dolby surround sound. However, in spite of these features, most reviewers agree that separate sound cards provide better audio quality.

Laptops usually have integrated sound capabilities on their motherboards or small sound cards. However, space and temperature control considerations make top-of-the-line internal cards impractical. So, laptop users can purchase external sound controllers, which use USB or FireWire connections. These external modules can significantly improve laptop sound quality. Analog vs. Digital Sounds and computer data are fundamentally different. Sounds are analog - they are made of waves that travel through matter. People hear sounds when these waves physically vibrate their eardrums. Computers, however, communicate digitally, using electrical impulses that represent 0s and 1s. Like a graphics card, a sound card translates between a computer's digital information and the outside world's analog information. The most basic sound card is a printed circuit board that uses four components to translate analog and digital information: • • • •

An analog-to-digital converter (ADC) A digital-to-analog converter (DAC) An ISA or PCI interface to connect the card to the motherboard Input and output connections for a microphone and speakers

Instead of separate ADCs and DACs, some sound cards use a coder/decoder chip, also called a CODEC, which performs both functions.

A sound card must translate between sound waves and bits and bytes

X-Fi One of the newest advances in sound card technology is X-Fi, or Xtreme Fidelity, from SoundBlaster manufacturer Creative. X-Fi features: • • • •

"Active Modal Architecture," which gives people different sound options for games, leisure use or music creation A Digital Signal Processor (DSP) with 51 million transistors Multiple processing engines, each of which performs specific sound operations A 24-bit Crystallizer, which reverses some of the sound quality loss inherent in 16-bit CD recording

ExtremeTech has a comprehensive article detailing X-Fi's features.

ADCs and DACs Imagine using your computer to record yourself talking. First, you speak into a microphone that you have plugged into your sound card. The ADC translates the analog waves of your voice into digital data that the computer can understand. To do this, it samples, or digitizes, the sound by taking precise measurements of the wave at frequent intervals.

An analog-to-digital converter measures sound waves at frequent intervals.

The number of measurements per second, called the sampling rate, is measured in kHz. The faster a card's sampling rate, the more accurate its reconstructed wave is.

If you were to play your recording back through the speakers, the DAC would perform the same basic steps in reverse. With accurate measurements and a fast sampling rate, the restored analog signal can be nearly identical to the original sound wave. Even high sampling rates, however, cause some reduction in sound quality. The physical process of moving sound through wires can also cause distortion. Manufacturers use two measurements to describe this reduction in sound quality: Total Harmonic Distortion (THD), expressed as a percentage Signal to Noise Ratio (SNR), measured in decibels For both THD and SNR, smaller values indicate better quality. Some cards also support digital input, allowing people to store digital recordings without converting them to an analog format. • •

Methods of Sound Creation Computers and sound cards can use several methods to create sounds. One is frequency modulation (FM) synthesis, in which the computer overlaps multiple sound waves to make more complex wave shapes. Another is wave table synthesis, which uses samples of real instruments to replicate musical sounds. Wave table synthesis often uses several samples of the same instrument played at different pitches to provide more realistic sounds. In general, wave table synthesis creates more accurate reproductions of sound than FM synthesis.

SPEAKERS

In any sound system, ultimate quality depends on the speakers. The best recording, encoded on the most advanced storage device and played by a top-of-the-line deck and amplifier, will sound awful if the system is hooked up to poor speakers. A system's speaker is the component that takes the electronic signal stored on things like CDs, tapes and DVDs and turns it back into actual sound that we can hear. In this article, we'll find out exactly how speakers do this. We'll also look at how speaker designs differ, and see how these differences affect sound quality. Speakers are amazing pieces of technology that have had a profound impact on our culture. But at their heart, they are remarkably simple devices. Most ordinary speakers use an electromagnet to push and pull on a cone-shaped diaphragm (see How Speakers Work for details). But there are a few other technologies on the market. The speakers you saw at your friend's house are probably electrostatic speakers.

Instead of using an electromagnet, electrostatic speakers vibrate air using a large, thin, conductive diaphragm panel suspended between two stationary conductive panels. These conductive panels are charged with electrical current from a wall outlet, creating an electrical field with a positive end and a negative end. The audio signal runs a current through the suspended diaphragm panel, rapidly switching between a positive charge and a negative charge. When the charge is positive, the panel is drawn toward the negative end of the field; when the charge is negative, it moves toward the positive end of the field. In this way, the diaphragm rapidly vibrates the air in front of it. Because the panel has such a low mass, it responds very quickly and precisely to changes in the audio signal. This makes for clear, extremely accurate sound reproduction. The panel doesn't move a great distance, however, so it is not very effective at producing lower-frequency sounds. For this reason, electrostatic speakers are often paired with a woofer that boosts the lowfrequency range. The other problem with electrostatic speakers is that they must be plugged into the wall and so are more difficult to place in a room.

Based on the varying electrical audio signal, the diaphragm is alternately charged with a positive current and a negative current.

The new sound cards

For many years PC sound has been totally dominated by the Sound Blaster card. All sound cards had to be compatible with Sound Blaster, or it would not sell. Obviously that is due to the numerous game programs, which require a SB compatible sound card. The new sound cards break away from the Sound Blaster compatbility. This break involves many facets. Below I will describe some of the tendencies in the sound technology. Sound over the PCI bus New sound cards use the PCI bus. The SB compatibility used to require the old ISA bus, but this has been overcome. Creative Labs produce fine PCI-based SoundBlaster cards. With PCI you gain these advantages:  The IRQ problems disappear.  Signal/noise ratio can be improved with 5 dB.  There is sufficient bandwidth (capacity for data transmission).  The sound card workload for the CPU is less.  We can drop the ISA bus, which takes up unnecessary space on the PC system board. The problem in moving the sound to the PCI bus involved the existing software. First of all the old DOS games, which expected and demanded the Sound Blaster card with its well-known IRQ- and DMA numbers. The games did not work with the new cards, unless special solutions were implemented. However, the impact of this problem is gone. No more ISAbased sound cards are in production, and all games use the new standards for Windows sound. Onboard sound chips Many motherboard include sound card functions. This is i fine thing, if you only need sound for ordinary use. The quality is not as good as the sound from a $80-$100 sound card, but for many users it is fine! On-board audio is found within some chip sets. For instance you find it in the much used VIA KT133 chip set for AMD processors. Here the VT82C686B south bridge I/O-controller holds built-in AC97 digital audio functions:

HEAD PHONES Head phonmes include a pair of speakers which are attached to an adjustabel strap that can be customfitted to the user’s head . Many computer users prefer listening to audio through head phones rather that using speakers. These devices are helpful when using portable computers, which do not have high quality speakers or playing audio might disturb others. Today even inexpensive head phones have reasonably high quality speakers are light weight and comfortable to wear. Headphones can be plugged into the out put jacket of sound card. A headset includes two speakers and a microphone plugged into the sound card in microphone input and speakers connect to sound card speakers jack. Headset replace both remote microphones and speakers and are useful for speech recognisation application, video conference and using the computers to make phone calls. Many different types of headphones are available in market now-a-days.There are wire headphones and wireless headphones.