14-10-2016, 10:26 AM
1458898521-CDDVDbyAaronRinacaMikeFerrisMikeBurkerSteveMathieu2001SPR.pdf (Size: 485.08 KB / Downloads: 4)
Compact Disk (CD) Basics
•Uses Digital Technology to store data in binary values of Zero and One
•Uses “Pits” and “Lands” to signify binary values
•CD’s Read at a Constant Linear Velocity (CLV)
•Capable of Storing Large Amounts of Data (up to 700MB)
•Uses Error Correction for reliable data retrieval even if the CD becomes
lightly scratched.
Types Of Compact Disks
CD Audio – The first type of CD that was available. This allows for
the storage of digital audio. These are playable in all current CD drives
and car audio systems including DVD players.
CD-ROM – Computer Data is stored on these units such as games,
applications, and other files. Only readable on computers.
CD-R – Allows users to write data once to a recordable Compact
Disk. Can not be re-written and can be read in all current players
depending on wither the disk holds Audio or Data.
CD-RW – Users Can Write and Re-Write these special disks.
However because of the disk format, they cannot be read in Audio CD
players or DVD players.
CD Audio: How Does It Work?
Sound is Sampled at 40,000 Times per Second or Higher
Each Sample Must be Represented by at least a 16-bit number
Therefore, with 40,000 samples per second, and 16-bits per sample,
that’s over 640,000 bits per second! Therefore a 1 minute long
music clip would take over 38,400,000 bits (+/- 38MB) for storage!
Computer CD-ROM’s
Divided Into Sectors Containing User Data and Error Correction Codes.
Set up similar to hard drives however they do not have a “FAT” sector,
instead sectors are opened and closed with special pit and land
combinations.
File Systems are used to store data for easy and quick access
CD-R Technology
Can Only Write Data Once
Uses Gold Instead of Aluminum for its Reflective Layer, thus a
higher cost than traditional CD’s
Uses Dye to “trick” the CD player Laser into thinking it is passing
over real Pits and Lands, when in actuality it is merely passing
over light and dark spots in the dye.
CD-RW Technology
Allows Users to Write Many Times (However This is Limited)
Uses Alloy of Sliver, Indium, Antimony, and Tellurium for Reflective Layer
Uses varying power levels to read and write lands and pits.
High Power = Creates Pits
Melts Alloy and Converts it to a High-reflectivity Crystalline state
Medium Power = Creates Lands
Melts Alloy and Converts it to Natural Crystalline state
Low Power = For Reading…no change to CD surface.
No Change in Alloy
Error Correction, Why Bother?
Error correction is an imperative part of CD technology, you cannot
take good enough care of a CD to prevent errors. Sony and Phillips
knew this, so they instituted the basics of Error Correction
Technology.
Errors can be caused by:
Manufacturing defects (Rare)
Scratches (Very Common)
Error Correction Types:
CIRC – (Cross Interleaved Read-Solomon Code) encoder
EFM Modulation – (Eight to Fourteen)
CIRC Error Correction:
Can correct Error Bursts up to 3,500 bits long (2.4mm in length)
Helps to compensate for Error Bursts up to 12,000 bits (8.5mm).
These types of errors are typically caused by minor scratches.
EFM Error Correction
Technology
Works to ensure Pits and Land Lengths are no Less Than 3 channel
bits and no More Than 11 Channel Bits
Very widely used in portable CD players because it helps to reduce
the skipping effect of jitter and distortions.