VCRS DVDS AND SERVICES

Nishant Mittal

MAEERS MIT PUNE

E&TC

Optical Disc Recording

• 1) VCD

• 2) DVD

• 3) MP3 Player

• 4) HD-DVDs( Not in Syllabus)

• 5) BD-DVDs(Not in Sylllabus)

• 6) Mpeg Player( Unit 3 DTV)

Magnetic Tape Recording: The Entertainment Begins

• Magnetic Tape records the sound and converts it into electrical signals through microphone.

• Alignment and orientation of tiny magnetic particles will depend upon the sound intensity and frequency of audio signal.

Numerical Analysis

• 1) Recorded wavelength

2) If the Gap width = max o/p obtained. Exceeding it would decrease the o/p

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Dolby’s Noise Reduction technique

• All weak signals irrespective of the frequencies need to be emphasized.

This is Dolby stereo system secrets

Part 2- VCD Players

Structure of a CD Disc

CD Burn? Why “burn”

• CD writing is done with the help of powerful laser beam

• The photo-resistive material is “burnt” in the form of ‘pits’ and digital data is recorded.

• Next step is A-D conversion

• Now laser beam modulated and pits are generated.

Optical assembly

VCR

The insight

• On the CD, right- and left-channel signals are recorded separately one after the other in a fixed time interval.

• This helps to suppress cross-talk between the right and the left channels, reproducing stereophonic sound.

• During playback the fine track is exposed to the laser beam.

• The playing of CD commences from the centre and continues towards the outer edge.

Motor assembly

Servos

The servo system consists of a set of servo systems that make thelaser beam accurately focus on the surface of the CD and trackacross the fine surface of the CD, when the CD is made to rotate ata correct speed.

• Most CD players have four individual servo systems, namely, 1) the focus,2) tracking,3) carriage,4) and spindle servos. • CD players with radial optical assembly have only three servo

systems, namely, 1) the focus,2) radial,3) and spindle servos.

Facts

• CD-RW is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser in this case is used to heat and alter the chemical properties of the alloy and hence change its reflectivity.

• A CD-RW does not have as great a difference in the reflectivity of lands and bumps as a pressed CD or a CD-R, and so many CD audio players cannot read CD-RW discs, although the majority of stand-

alone DVD players can.

Why CD

• 1) Read with help of laser. No direct touch if the pick up tip hence less chance of scratches.

• 2) DIGITAL- That’s the main advantage

• 3) Flat frequency response (20 Hz – 20 kHz)

• 4)Error Correction ( Circ encoding)( Refer Sklar’s book digital communication)

• 5) Wow and flutter distortion absent

DVD

• Digital video disk or digital versatile disk (DVD) is a type of opticaldata storage medium capable of holding up to 17 giga-bytes (GB) ofinformation.

• DVDs can produce such high quality pictures and sounds, they areexpected to eventually replace both VCRs and CD players. It isanticipated that the market for DVD players will reach 10 millionunits by the year 2000.

• The key innovation that makes DVDs superior to CDs is the laserused to read and create the pits. DVDs use a shorterwavelength,red laser that can place pits more densely on the surfaces of thedisks. This not only allows for more data, it also requires that thedisks be only half as thick as conventional CDs. Consequently, twolayers can be bonded together to create a double-sided disk whichhas the same thickness as a CD (1.2 mm).

DVD

High Storage capability

Backward compatibility

interoperability

Transition of vcd to dvd

• DVD disks also look like CD-ROMs, but the data is packed together more tightly. The surface of the disk is coated with a reflective silver layer that is protected by a thin, hard coating of lacquer.

• If a semitransparent gold layer is put on top of the reflective silver layer, the disk can be made to store 2 layers of data on one side.

• By using less power, the laser can read the data from the gold layer first and then by increasing the power, it can read the silver layer. This nearly doubles the capacity of one side to 8.5 GB.

Cont.

Finally the differences

Parameters VCD DVD

1) Material Used Plastic Plastic

2) Immunity to scratches Immune Immune

3) Diameter,thickness 120 mm,1.2 mm 120 mm, 1.2 mm

4) Pitch for tracks 1.6um 0.74um

5) Minimum pit length 0.834um 0.4 um

6) Capacity 700 Mb 4.7 Gb

7) Resolution PAL(India) 352*288 720*576

8) Video Compression MPEG-1 MPEG-2

9) Compatibility Good Very Goof

Quality Good Best

Next era----- Blue Ray Discs

Thank you!!!!!

“Do not buy Pirated DVDS and VCDS”