webpointmorpheus Computer Info
Sound, Video, & CRT

     Overview      Sound      Video      Display Adapters      CRT      Dot Pitch      LCD

©2005 - material compiled by Bob Carnaghi, www.webpointmorpheus.com

Overview     Top of Page

This document considers two human sensory areas (hearing and sight) that are also two primary output areas of the computer: sound and video. The technical evolution of these areas with regards to the computer has kept pace well with other developments in the industry. The earliest PCs had a video resolution of 320 x 200 and were monochrome or 4 color. The most recent digital monitors require absolutely no user configuration and have millions of colors. That's quite an evolutionaly process for about 20 years. The evolution of sound as output by a computer is similarly remarkable, not the least consideration being the ongoing copyright litigations with the music industry. Additionally, the availability of surround sound is truly remarkable in quality.

Computer Sound     Top of Page

Computer sound must be processed through a sound card in order to become audible. Sound cards can be considered for five basic parameters:

1. Processor capabilities - determines how much of sound generation must be burdened by the system CPU.
2. Speaker support - stereo, surround, sub-woofers, etc.
3. Recording quality - higher quality devices will reduce noise from input devices.
4. Jacks - Line Out, Line In, Rear Out, Analog/Digital Out, Microphone, Joystick, etc.
5. Extra features - integration with home entertainment centers, external input devices, etc.

More About Computer Sound     Top of Page

Every sound card comes with a processor, and can produce sounds of some form and quality. Sound quality or sound depth is measured in bits. The deeper or more fatihful the sound recording, the more the sound must be sampled, the more bits of information must be saved. An 8-bit sample (2⁸) captures 256 sound characteristics. In contrast, a 16-bit (2¹⁶) sample captures 65,536 sound characteristics. The most popular sound player today is the Windows Media Player.

Video     Top of Page

Video is technically considered as an output of the computer. In essence, it is the prime output, as the user can see visually all that is going on inside the computer on the screen. Computer video monitors break into two broad categories: CRT and LCD (see below.) Listed below is an overview of some introductory concepts regarding computer video.

Display Adapters     Top of Page

Also called Video Cards are the means by which digital information is output from the CPU and other computer peripherals and displayed on the screen for viewing.

Types of Display Adapters
Type	Description
MDA (Monochrome Display Adapter)	First video card, designed for monochrome monitors
CGA (Color Graphics Adapter)	First video card that was designed for a color monitor (4 colors)
EGA (Enhanced Graphics Adapter)	Supported 16 colors
PGA (Professional Graphics Adapter)	First video card capable of 3-D displays
VGA (Video Graphics Adapter)	Repalced PGA and provide 640 x 480 @ 16 colors
SVGA (Super VGA)	Same as VGA but provides unlimited colors

CRT     Top of Page

CRT (Cathode Ray Tube) is the display type that is large, bulky, prolific, and appears similar to a television picture tube. This technology is rapidly becoming eclipsed by digital technology (LCD, see below) which is easier to work with, sharper, more compact, and more faithful in color and resolution. The CRT produces images by means of an electron gun at the back of the tube which fires a stream of electrons onto a phosphor coated screen which have been manipulated with a yoke coil. The refresh rate determines how many times the electron gun makes a full traverse through the entire screen.

Parts of the CRT
Part	Description
Electron Gun	The device at the back end of the CRT which shoots electrons toward the screen display
Phosphor Coating	The coating at the display end of the CRT which is struck by the electrons and becomes visible light
Yoke	The ring of electromagnets that controls the impact point of the electrons on the phosphor coating.
Shadow Mask	A thin screen in front of the phosphor coating that precisely defines each dot.

Dot Pitch     Top of Page

Dot Pitch is the diagonal distance between phosphorous dots of the same color. Imagine the screen being filled with a continuous array of red, green, and blue dots grouped into triads. The activation of a color, or a combination of the colors is what renders color images. When a monitor is given a 'Dot Pitch' rating, this is the diagonal measurement to the closest similarly colored dot. The smaller the number, the more the dots on the screen, the more color the monitor is capable of rendering.

LCD     Top of Page

LCD (Liquid Crystal Display) technology is vastly different from CRT technology. There are several advantages to LCD technology, which include lower operating voltages, compact size, portability, etc. They are thinner and lighter, virtually flicker-free, and don't emit the potentially hazardous radiation that is common from the CRT. There are several drawbacks to LCD technology which are not present in CRT technology. LCD screens tend to be sensitive to freeze-thaw, don't fare well in direct sunlight, and are more sensitive to damage by handling and touch than CRT monitors.

LCD screenw operate on the principle of polarized light. The screen is constructed of a matrix of horizontal and vertical electrodes that are individually controlled electronically. Polarized plates are placed at the front and back of the screen and create a sandwich effect of the display materials. Each junction of a horizontal-vertical element creates a screen pixel. When a voltage is applied to a specific pixel, the molecules in the liquid crystal align to pass light through the polarizer. With the addition of color technology, these displays take on a marvelous viewing depth.

Early LCD technology incorporated a dual scan or passive matrix construction. Each electrode was turned on/off individually, and the power consumption for these units was very low. Current construction incorporates a collection of transistors (Thin Film Transistor) to control each pixel which creates the active matrix construction. This is the most popular LCD type at the time of this writing.

Modern digital graphics adapters working with LCD monitors relieve the user of any need to control the screen resolution or other display settings. The screen resolution of an LCD monitor is pre-determined by the number of electrodes that are built into the unit. This is a radically different approach than the typical CRT adjustment procedure.