Lecture



Addendum for Week 18


  • Multimedia on a PC


Sound


This is a typical sound wave. Computers cannot use this information as a computer only speaks ones and zeros. Therefore, computers need to have the above sound wave converted into those ones and zeros. This is done by assigning binary codes of 8 bita to various voltages. For example, a 4.2 volt signal may be assigned the value of 1001 0001.

(number just chosen at random). A process of sampling is done to measure the voltage level at eight thousand times a second. These voltage levels are assigned numerical values as above. Therefore 1 second of sound corresponds to 8k bytes.


Sound Cards


Sampling is how the conversion from analog to digital is accomplished

Sampling is done at the speed of either 8 or 16 bits

Sampling rate must be at least 2 times the original in order to accurate reproduce signal

Sampling rate of CDs is 44,100 Hz

8 bit sampling creates range of bits from -128 to +127 (255 total) plus 0 no sound

16 bit sampling creates 65,536 bit values -32768 to +32769 plus 0 for no sound


External Ports on a typical Sound Card



Internal connections on a typical sound card




Sound cards must have a software driver to operate

A new sound card typically comes with a driver disk but searching the internet for the driver may be required.


Compression – sound has a lot of extraneous noise and silence associated with it when recorded. To minimize the amount of memory required for a sound, compression is used


MPEG (Motion Picture Experts Group) developed a system where the computer device only records the changes that occur from one frame to the next (background rarely changes for example). There are currently four standards listed below:


  • MPEG-1 standard

    • Image compression for business/home applications

  • MPEG-2 standard

    • Video film compression on DVD-ROM

  • MPEG-3 standard

    • Audio compression

  • MPEG-4 standard

    • Video transmissions over the Internet


Optical Storage Technology


CDs use tiny pits or lands on the surface of the CD to record sound, data or video. CDRoms use CDFS (CD file system) or UDF (Universal Disk Format)

CDRoms are record once only media. Data is physically burned into the surface and cannot be changed nor written over.

CDs store data as pits – unused areas are called lands

Use both Constant linear velocity for head speed or Constant angular velocity – Speed of the head changes the closer the head gets to the center of the CD


Surface is spiraled and is 3.5 miles long

Data played back by amount of light reflected off the surface as read head passes over the surface


Speed of a CD reader is measured as multiples of the first CDs which was 150kbs




Installing a CD is the same physical installation as any IDE device but one must remember to check the jumper for proper position





DVDs

DVDs use MPEG 2 compression, write on both sides of a disk, and are installed identically to CD players and other IDE devices

DVDs come in a variety of devices such as:


DVDs require a decoder card if system is older. Newer models do not require such a card.


Tape storage – older Technology but still prevalent in many areas

Tape drives may be internal (ATAPI) or external (SCSI) are inexpensive don’t hold a lot of data

Storage area networks use Tape technology to record daily or weekly or monthly backups of important company data. SAN is a very profitable business to get into – many use tapes for the backup


RAID disks


Simple volume – single disk

Spanned volume – appears to computer as a single disk but actually spreads data over multiple disks

Striped (RAID 0) – two drives with parts of the data on both

Mirrored (RAID 1) – data is written to multiple disks at the same time creating copies of the original automatically

RAID 5 – striped that uses parity checking – servers only


Available in 2000 and XP and NT



Flash drives – new devices that are amazing


What is a MASER?

MASER stands for Microwave Amplification by Stimulation Emission of Radiation. A LASER is a MASER that works with higher frequency photons in the ultraviolet or visible light spectrum (photons are bundles of electromagnetic energy commonly thought of as "rays of light" which travel in oscillating waves of various wavelengths) .