Optical discs

[seriously disabled]

Optical disc technology is a topic I never understood. How do the microscopic bumps in the optical disc contain data?

[Cap'n Refsmmat]

Think about it this way:

 

Morse code works through having two different types of "signal": dot and dash. Mix up the dots and dashes in different orders and they represent different things.

 

The same applies to the optical disc. As you spiral in from the outside of the disc toward the inside, there can be two kinds of "signal": pit or no pit. (The laser reflects differently off of each, making it apparent to the CD drive which kind each is.) The combinations of pit and no pit decide what information is on the disc.

 

(Except instead of Morse code it's all in binary, of course.)

[seriously disabled]

The same applies to the optical disc. As you spiral in from the outside of the disc toward the inside, there can be two kinds of "signal": pit or no pit. (The laser reflects differently off of each, making it apparent to the CD drive which kind each is.) The combinations of pit and no pit decide what information is on the disc.

 

(Except instead of Morse code it's all in binary, of course.)

 

But in DVDs how does the DVD player convert the laser light into video images? Does it convert it into electrical signal first?

[insane_alien]

yep, same thing as happens in CD's pretty much.

 

you have a big long stream of binary information. the laser refelcts off the disk and onto a sensor which converts it into an electrical signal which a program on the pc/dvdplayer/whatever interprets into video and sound.

[seriously disabled]

you have a big long stream of binary information.

 

What I don't understand is how is this binary information realized or expressed in the pits and bumps on the DVD plastic? Since binary information is not a physical thing so how is it expressed on the DVD plastic?

 

Also I thought that only a computer can read binary information so is there a computer in the DVD player?

[insane_alien]

well, capn answered that bit, there are pits on the disk. light will reflect off the disk surface well if there is no pit and if it has a pit then it will not reflect so well.

 

now, there are two signals that can be coming from the sensor, pit or nopit which corresponds with 0 and 1. which is binary.

 

and binary information can be 'read' by pretty much any electronic device with a transistor in it. there are integrated circuits in a dvd player specifically to decode the video stream and handle the menu functions, they are not very powerful but they could be classed as computers.

[Ibeamer]

Any digital stream which encodes audio or video data must be converted to analog data before it becomes intelligible to a human. Human ears and eyes are analog devices.

An electronic circuit called an "analog to digital converter" (ADC) is fed the binary data from the source where is converted to a varying voltage or current (AC signal) and then amplified and directed to a transducer, such as a speaker or a display device, which converts it to a signal meaningful to human senses.

In between the digital signal and the ADC is a device called a "codec", which is usually implemented in software that knows how to break up the binary bit stream into the "chunks?" to go to the ADC. (Yes there a microprocessor (small computer) built into CD / DVD players).

Edited January 2, 2009 by Ibeamer
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