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Chapter 7 Input / Output Technology. Chapter Goals. Describe manual input devices and how they are implemented. Describe concepts of text and image representation and display, including digital representation of grayscale and color, bitmaps, and image description languages.

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chapter goals
Chapter Goals
    • Describe manual input devices and how they are implemented.
    • Describe concepts of text and image representation and display, including digital representation of grayscale and color, bitmaps, and image description languages.
  • Explain the characteristics and implementation technology of video display devices.
  • Understand printer characteristics and technology.
  • Identify the characteristics of audio I/O devices, and explain how they operate.

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chapter topics
Chapter Topics
  • Describes the concepts, technology and hardware used in communication between people and computers.
  • Understand the importance of I/O technology.

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manual input devices
Manual Input Devices
  • Keyboard Input
  • Pointing Devices

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manual input devices1
Manual Input Devices

Keyboard Input

  • Keyboard devices translatekeystrokes directly into electrical signals.
  • A keyboard controller is used to generate bit stream outputs according to an internal program or lookup table.
  • A keyboard controller generates an output called a scan code.
  • A scan code is a one or two-byte data element that represents a specific keyboard element.

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manual input devices2
Manual Input Devices

Pointing Devices

Translates the spatial position of a pointer, stylus, or other selection device into numeric values within a system of two-dimensional coordinates.

  • Mouse
  • Trackball
  • Joystick
  • Digitizer Tablet

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manual input devices3
Manual Input Devices

Mouse – a pointing device that is moved on a flat surface such as a table, desk or rubber pad.

Trackball – a mouse with the roller ball on the top. The roller ball is moved by the fingertips, thumb or palm of the hand.

Joystick – used as an input device with computer games.

Digitizer Tablet – uses a pen, or stylus, and a digitizing tablet. The tablet is sensitive to the placement of the stylus at any point on its surface.

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basic concepts of print and display
Basic Concepts of Print and Display
  • Sharing features of printing & videotechnologies
    • Character representation methods
    • Measurement systems
    • Methods of generating color
  • Matrix-Oriented Image Composition
    • Fonts
    • Color
    • Pixel Content
    • Image Storage Requirements
    • Image Description Languages

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basic concepts of print and display1
Basic Concepts of Print and Display

Matrix-Oriented Image Composition

  • Display surfaces commonly are LCD, Flat Panel, Cathode ray tubes (CRT), or Paper
  • Display surfaces can be divided into rows and columns similar to a large table or matrix.
  • Each cell in the table represents one component of the image.

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basic concepts of print and display2
Basic Concepts of Print and Display

Matrix-Oriented Image Composition

  • One of the cells is a pixel (Short for Picture Element).
  • Number of pixels in display area =F(display area size–HxW, pixel size)

Eg:

  • Find Number of pixel in a 19” flat panel display.
    • Pixel size:0.25mm2
    • Display size: 11”(28cm)x14.5”(37cm)”
      • Therefore No. of pixels: 28x(10)x37x(10)/0.25 = 414,400
      • For 0.24mm2
      • 28x(10)x37x(10)/0.24 = 431,666

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basic concepts of print and display3
Basic Concepts of Print and Display
  • The resolution of the display is:

The number of pixels displayed per linear measurement unit.

  • Example: 40 pixel/cm or = 100 pixel/in

Resolutionis stated in: dots per inch(dpi).

(Dot is equivalent to a pixel)

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basic concepts of print and display4
Basic Concepts of Print and Display
  • Higher resolution correspond to smaller pixel size which makes better quality because smoother curves incorporate into the image
  • Higher resolution = smaller pixel size = higher quality of print or display

Two resolutions displaying the same text

Top: 50 dpi and bottom: 200 dpi

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basic concepts of print and display5
Basic Concepts of Print and Display

Matrix-Oriented Image Composition

  • dpi is used to indicate resolution for printers and monitors. But is more popular in US and specially for printers.
  • Printer resolutions are between 125 to 600 dpi
    • 125 dpi is for a low quality dot matrix printer
    • 600 is for a laser or ink-jet printer
  • Typesetting equipment have a resolution of 1000-2000 dpi.

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basic concepts of print and display6
Basic Concepts of Print and Display

Matrix-Oriented Image Composition

  • Image size is stated (measured) in pixel: HeightxWidthor RowxColumn Or: 300x200
  • The image size depends on pixel size
  • If pixel size is 0.3 mm the above image size is 90mmx60mm
  • If pixel size is 0.25 mm the size of the above image is 75mmx50mm

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basic concepts of print and display7
Basic Concepts of Print and Display

Matrix-Oriented Image Composition

  • Point = (1/72) inch is adapted as the standard pixel size for printers.
  • This measure is used today in spite the fact that printers can apply ink pixels smaller that (1/1000) of an inch.

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basic concepts of print and display8
Basic Concepts of Print and Display

Matrix-Oriented Image Composition

  • Dot pitch: is a measure of monitors and printers resolution. Dot pitch is the vertical distance between pixels in (mm).
  • In monitors, it is a measure of image clarity.
  • A smaller dot pitch generally means a crisper and sharper image
  • This measure is more popular for monitors.
  • High quality monitors have dot pitch of less than 0.28mm
  • Current range of dot pitch is 0.24mm – 0.28 mm

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basic concepts of print and display10
Basic Concepts of Print and Display
  • Font – a collection of characters of similar style and appearance.

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Basic Concepts of Print and Display
  • Common unit for measuring font size is points.

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Basic Concepts of Print and Display
  • The measure of point refers to the height of the characters but not their width. The width is scaled to match the height.
  • Characters vary in height and placement. E.g. T is taller than a, and P & Q extend below the text baseline.
  • A font size is the distance between the top of the highest and bottom of lowest character in the font (e.g. T & p or q).

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basic concepts of print and display13
Basic Concepts of Print and Display

Color:

The human eye interprets different light frequencies as different colors.

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basic concepts of print and display14
Basic Concepts of Print and Display

Color for video

  • For video displays, color is generated directly by the display device.
  • The video display industry has used red, green, and blue as primary colors (RBG).
  • A video display that generates color uses mixtures of these colors.
  • Video display colors are called additive colors.

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basic concepts of print and display15
Basic Concepts of Print and Display

Color for print

  • For print, color is light frequency reflected from the paper.
  • The printing industry generates color using the inverse of the primary video display colors.
  • Printing colors are called subtractive color (CMY).
    • Subtracting colors are cyan (absence of red), magenta (absence of green), and yellow (absence of blue).

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basic concepts of print and display16
Basic Concepts of Print and Display

Pixel Content

  • Pixel content must be described digitally in bits.
  • The number of bits required to describe a pixel depends on color (monochrome, grayscale, or color).
  • A stored set of digital numbers describing a pixel is called a bit map.

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basic concepts of print and display17
Basic Concepts of Print and Display

Pixel Content

  • Monochrome use 1 bit.

0=back, 1=white

  • Grayscale using 3 bits produce 8 shades of gray (23=8).
  • Grayscale using 8 bits produce 256 shade of gray (28=256)including pure black and pure white.

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Basic Concepts of Print and Display

Pixel Content

  • Chromatic depth or resolution:

Refers to the number of distinct colors or gray shades that can be displayed.

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basic concepts of print and display19
Basic Concepts of Print and Display

Pixel Content

  • For color display, three separate set of bits are required to represent different intensity of additive (RGB) or subtractive (CMY).
  • Example: Color display using 24 bits uses 8 bits to represent intensity of each color (0-255) in additive or subtractive color scheme.
  • 255:0:0  bright red
  • 255:255:0  light magenta
  • 127:63:0  Brown
  • The number of distinct colors (chromatic depth) is 2(3x8) = 16 million

Color display with less than 24 bits cause each primary color be represented by less than 8 bits, causing a problem as computers deal with Byte size data more efficiently.

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basic concepts of print and display20
Basic Concepts of Print and Display

Pixel Content

  • Alternatively palette is use to display colors
  • A palette is a table of colors.
  • A palette of 8 bits can display 28=256 colors.
  • A palette of 4 bits can display 24 =16 colors.
  • In this case the intensity of each primary color will be FIXED. E.g. 127:255:127  light green

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basic concepts of print and display22
Basic Concepts of Print and Display

Pixel Content

  • Color can also be produced using dithering.
  • Dithering places small dots of different colors in an interlocking pattern. Human eye interpret this as uniform color representing a mixture of the dot colors.
  • 50% red + 50% blue  interpreted as magenta
  • 50% black + 50% white  interpreted as gray
  • Dithering is used in devices not capable of applying fine differences in color.
    • e.g. an ink-jet that only produces 4 different amounts of a single dye in one pixel area, produce 43=64 colors. Using dithering can simulate several shades between each of 4 colors.

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slide31

Basic Concepts of Print and Display

Dithering:

A technique used in computer graphics to create the illusion of varying shades of gray on a monochrome display or printer, or additional colors on a color display or printer. Dithering relies on treating areas of an image as groups of dots that are colored in different patterns.

Akin to the print images called halftones, dithering takes advantage of the eye's tendency to blur spots of different colors by averaging their effects and merging them into a single perceived shade or color. Depending on the ratio of black dots to white dots within a given area, the overall effect is of a particular shade of gray. Dithering is used to add realism to computer graphics and to soften jagged edges in curves and diagonal lines at low resolutions

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basic concepts of print and display23
Basic Concepts of Print and Display

Image Storage Requirements

  • Image storage requirements apply to images stored in primary and secondary storage, and to buffers used in I/O devices.
  • Image storage requirements can be reduced with image compression techniques.

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basic concepts of print and display24
Basic Concepts of Print and Display

Image Storage Requirements

Compression Techniques:

  • Graphics Interchange Format (GIF)
  • Joint Photographic Experts Group (JPEG)
  • Moving Pictures Experts Group (MPEG)

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basic concepts of print and display25
Basic Concepts of Print and Display

Image Description Languages

  • Use a symbolic language to describe primitive image components.
  • Can use a vector list.
  • Describe the image components that are straight-line segments or can be built from segments.

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technology focus postscript1
Technology Focus - Postscript

x= 245

y= 365

x= 340

y= 365

x= 245

y= 265

x= 340

y= 265

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video display
Video Display
  • Character-Oriented Video Display Terminals
  • Graphic Video Display Devices
    • CRTs
    • Flat Panel Displays

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video displays
Video Displays

Character-Oriented Video Display Terminals

  • Commonly used during 1970s and 1980s.
  • Terminal – consists of an integrated keyboard and television screen.
  • Used primarily today in systems such as retail checkout counters and factory floor environments.

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video display1
Video Display

Functional components of a video display terminal (VDT)

The display driver contained relatively simple electronic circuitry that translated ASCII/EBCDIC into a corresponding pixel matrix then passed to the display generator.

In modern VDTs, the display driver is an embedded computer with its μp, RAM & ROM.

Communication controller has changed from a slow serial port to USB, IEEE Firewire, or Ethernet.

Network computer or thin client was a hybrid device with a mix of VDT and microcomputer developed by Wyse Technology in 1990s

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video display2
Video Display

Graphic Video Display Devices

  • Used for displaying diagrams such as construction blueprints, wireframe models, writing diagrams and to produce mathematical graphs.
  • By the mid-1980s, monitors were manufactured.
  • Monitors operate as independent devices under control of a video controller attached to the system bus.

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video display3

Transfer of video data from the primary storage to the monitor.

Video Display

A modern video display (monitor) is connected to a video controller which is attached to the system bus.

The video controller accepts commands and data transmitted via a bus from the CPU and generates a TV-style analog video signal which is transmitted continuously to the monitor.

Video controller with monitor and bus connections

Similar to Cache but has differences, Video RAM, VRAM

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video display4
Video Display

Video Controllers

  • Enables communication between computer system and monitor
    • Accepts commands and data transmitted via a bus from the CPU
    • Generates analog or digital video signals, which are transmitted to the monitor
  • Terms:
    • Refresh cycle and refresh rate; video RAM; dual porting; graphics accelerators
video display5
Video Display

CRT

  • Current monitors are implemented using cathode ray tubes (CRT).
  • A CRT is an enclosed tube.
  • An electron gun in the rear of the tube generates a stream of electrons.
  • Pixel illumination is controlled by pulsing the electron beam.
  • The number of times per second that the entire surface is scanned by the electron gun is called the refresh rate.

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video display6
Video Display

Flat Panel Display

  • Liquid Crystal Display – is a flat panel matrix that consists of encapsulated liquid crystals sandwiched between two polarizing panels.
  • Active Matrix Display – Uses one or more transistors for every pixel.
  • Passive Matrix Display – shares transistors among rows and columns of pixels.
  • Electroluminescent Displays – similar to construction of LCDs. Color is generated with three matrices of different colored phosphors.

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video monitors
Video Monitors
  • Separate from keyboards
  • Common types
    • Cathode ray tubes (CRTs)
    • Flat panel displays
    • Liquid crystal displays (LCDs)
    • Plasma displays
    • LED displays
slide47
LCD
  • Contains matrix of liquid crystals sandwiched between two polarizing filter panels
  • Active and passive matrix displays
  • Manufactured with thin film transistor (TFT) technology
slide48

FIGURE 7.9 Light entering the rear filter can’t pass through the front filter if the liquid crystal is electrically charged (top); removing the charge returns the liquid crystal to its twisted state, allowing light to pass (bottom)

Courtesy of Course Technology/Cengage Learning

plasma displays
Plasma Displays
  • Combine elements of CRT and LCD technology
  • Flat panel, active matrix devices
  • Actively generate colored light near surface of the display
    • Good brightness and viewing
  • Require more power than LCDs
slide50

FIGURE 7.10 A plasma display pixel

Courtesy of Course Technology/Cengage Learning

printers and plotters
Printers and Plotters
  • Dot Matrix Printers
  • Ink-Jet Printers
  • Laser Printers
  • Plotters

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printers
Printers

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printers and plotters1
Printers and Plotters

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inkjet printers
Inkjet Printers
  • Most common printing technology
  • Prints with liquid ink placed directly onto paper
  • Uses mechanical movement or heat to force ink out of nozzle
  • Paper is drawn past moving print head
  • Resolution is up to 600 dpi

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printers and plotters2
Printers and Plotters

Dot Matrix Printers

  • Generate images through mechanical contact with ink and papers.
  • Character codes received by the print generator are transmitted as a series of control commands to the print head.
  • Characters are generated one or two vertical rows at a time.

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printers and plotters3
Printers and Plotters

Ink-Jet Printers

  • Uses a paper movement mechanism similar to that of a dot matrix printer.
  • The print head of an ink-jet printer consists of: an ink cartridge, a set of ink chambers and a set of ink nozzles.

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printers and plotters4
Printers and Plotters

Ink-Jet Printers

  • Each ink nozzle can print a single pixel and nozzles are arranged in short vertical rows similar to those of a dot matrix printer.

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slide58

An inkjet printer has disposable print cartridges that contain ink reservoirs, a matrix of ink nozzles, and electrical wiring and contact points.

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printer communication
Printer Communication
  • Impact printers
    • ASCII or Unicode characters
  • Inkjet and laser printers
    • Use pixels as fundamental output unit
    • Have relatively large buffers
  • IDLs are commonly used to improve printer performance

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printers and plotters5
Printers and Plotters

Laser Printers

  • Operates differently from other types of printers.
  • No print head or ink ribbon is used.
  • An internal image of the entire page is stored in an internal buffer as a bit map.
  • Once filled, the buffer contents are sent to the print driver for generation.

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printers and buffers
Printers and Buffers

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slide62

Printers and Buffers

  • A rotating metal drum is lightly charged over the width of its surface.
  • The print driver reads rows of pixel rows of pixel values from the buffer and modulates a tightly focused laser over the width of the drum.
  • The drum is advanced, and the process is repeated with the next line of pixels.
  • The laser removes the charge wherever it shines on the drum. The drum contains an image of the page, with charged areas representing black pixels and uncharged areas representing white pixels.
  • After charging, the drum then passes a station where fine particles of toner (a dry powder ink) are attracted to the charged areas.
  • 6. In synchronized motion with the drum, paper is fed through a series of rollers and given a high electrical charge. As the paper passes over the drum surface, toner on the drum is attracted to the paper because of its higher charge.
  • The paper and attached toner are fed through heated rollers that fuse the toner to the paper surface.
  • A light source removes all charges from the drum, and excess toner is removed from the drum by a fine blade and/or vacuum.

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slide63

Printers and Buffers

Laser printers operate with an electrical charge and the attraction of ink to that electrical charge.

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printers and plotters6
Printers and Plotters

Plotters

  • A printer that generates line drawings on wide sheets or rolls of paper.
  • Paper is mounted within a paper control mechanism that can move the paper up or down precisely.
  • Can handle paper widths up to 60 inches.

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optical input devices
Optical Input Devices

Optical scanning devices can be differentiated by the following criteria:

  • Input format requirements
  • Normal and maximum spatial resolution
  • Normal and maximum chromatic resolution
  • Embedded processing capacity

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optical input devices1
Optical Input Devices

Mark Sensors and Bar Code Scanners

  • Mark Sensors – scans for light or dark marks at specific locations on a page.
  • The mark sensors uses preprinted bars on the edge of the page to establish reference points.

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optical input devices2
Optical Input Devices

Mark Sensors and Bar Code Scanners

  • A scanning laser sweeps a narrow laser beam back and forth across the bar code.
  • Bars must have precise width and spacing, as well as high contrast for accurate decoding.

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optical input devices3
Optical Input Devices

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optical input devices4
Optical Input Devices

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optical input devices5
Optical Input Devices
  • Optical Scanners – generate bit map representations of printed images.
  • A bright light is shone on the page and reflected light is detected by an array of photodetectors.
  • Spatial resolution is determined by the size and spacing of the photodetectors.

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optical input devices6
Optical Input Devices

Optical character recognition (OCR)

  • Combine optical scanning technology with hardware or software interpretation of bit map content.
  • The bit mapped representation is searched for patterns corresponding to printed characters.

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optical input devices7
Optical Input Devices

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audio i o devices
Audio I/O Devices

Sound generation and recognition can be used in a number of ways.

  • General-purpose sound output, such as warnings, status indicators, and music
  • General-purpose sound input, such as digital recording
  • Voice command input

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audio i o devices1
Audio I/O Devices

Sound generation and recognition can be used in a number of ways.

  • Speech Recognition
  • Speech Generation

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audio i o devices2
Audio I/O Devices

Speech recognition

  • The process of recognizing and appropriately responding to the meaning embedded within human speech.
  • Human speech consists of individual sounds called phonemes.

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audio i o devices3
Audio I/O Devices

A number of factors complicate the process of speech recognition:

  • Speaker variability
  • Phoneme transitions and combinations
  • Real-time processing

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audio i o devices4
Audio I/O Devices

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audio i o devices5
Audio I/O Devices

Speech Generation

  • A device that generates spoken messages based on textual input is called audio response unit.
  • Simple audio response units digitally store and play back words or word sequences.

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audio i o devices6
Audio I/O Devices

Speech Synthesis

  • Individual vocal sounds, or phonemes, are stored within the system.
  • Character outputs are sent to a processor within the output unit, which assembles corresponding groups of phonemes to generate synthetic speech.

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general purpose audio hardware
General-Purpose Audio Hardware

Common names for general-purpose audio hardware are:

  • sound card
  • sound board
  • multimedia controller

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general purpose audio hardware1
General-Purpose Audio Hardware

Sound cards include:

  • an analog-to-digital converter (ADC)
  • a digital-to-analog converter
  • a low power amplifier
  • connector for the microphone
  • a speaker or headphones

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general purpose audio hardware3
General-Purpose Audio Hardware

Musical Instrument Digital Interface (MIDI) – is a standard for storage and transport of control information among computers and electronic instruments.

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summary
Summary
  • Manual input devices include keyboards, mice and other pointing devices.
  • Display surfaces can be divided input rows and columns similar to a large table or matrix.
  • A stored set of numeric pixel descriptions is called a bit map.

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summary1
Summary
  • Video display terminals consist of an integrated keyboard and television screen.
  • Commonly used paper output devices include dot matrix printer, ink-jet printer, laser printers, and plotters.

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summary2
Summary
  • Optical input devices include optical scanners, mark sensors, bar code readers, and optical character recognition devices.
  • General-purpose speech recognition systems can be used for command and control, or for the input of large amounts of textual material.
  • Sound cards include converters, amplifiers, microphone, speaker and headphone connectors

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