Unit-II Audio Systems -12 Marks - PowerPoint Presentation

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Unit-IIAudio Systems

-12 Marks

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Course Outcome

Maintain Audio Systems

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Introduction

A compact disc, or CD, is an optical storage medium with digital data recorded on it. The digital data can be in the form of audio, video, or computer information. When the CD is played, the information is read or detected by a tightly focused light source called a LASER (thus the name optical medium). This article will focus on audio compact discs, which are used to play back recorded music.

By the late 1970s, a common set of standards for the optical storage discs had been developed by the joint efforts of Sony and Philips.

A consortium of 35 hardware manufacturers agreed to adopt this standard in 1981 and the first compact discs and

compact disc players

were introduced in the market in 1982.

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What is a CD?

A compact disc is a thin, circular disc of

metal

and

plastic

about 12cm (just over 4½ inches) in diameter.

It's actually made of three layers. Most of a CD is made from a tough, brittle plastic called polycarbonate. Sandwiched in the middle there is a thin layer of

aluminum

. Finally, on top of the aluminum, is a protective layer of lacquer. The first thing you notice about a CD is that it is shiny on one side and dull on the other. The dull side usually has a label on it telling you what's on the CD; the shiny side is the important part. It's shiny so that a

laser

beam can bounce off the disc and read the information stored on it.

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Construction of Compact disc

Storage area

15mm 33mm

1.2mm

Disc thickness

50mm

116mm 120mm

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On one side of the disc the audio signals are recorded on other side label ,indicating contents of the disc are printed.

v

Label side

Recording side or

Audio data

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Size and capacity-

Diameter-

4.75 inch(120mm

)

Whole to insert CD-

15mm

Actual storage area-

33mm circular

Disc thickness-

1.2mmA standard CD can store up to 74 minutes of data i.e. audio information However, most CDs contain only about 50 minutes of music, all of which is recorded on only one side of the CD (the underside).

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Material used

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Block Diagram of CD Player

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Components of CD Mechanism

CD pick-up assembly

CD Lens:

- Collimation Lens

- Concave Lens

- Objective Lens

- Cylindrical Lens

3. Drive motors

- Tray, loading motor

- Slide, sled, feed motor - Spindle, disc, turntable motor4. Gear system

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Pick –Up assembly

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Pick-up Assembly

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Lenses used in CD Player

1.Collimation Lens

2. Objective Lens

3. Concave Lens

4. Cylindrical lens

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Collimation

Lens

It is used to produce completely parallel beams of LASER.

This lens together with objective lens is used to focus the laser beam to the disc surface.

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Objective Lens

It is used to focus the LASER beam onto the CD surface and to receive the reflected beam.

It sharpens the beam and focus exactly at the center of CD track using focus and tracking coil.

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Concave Lens

This concave lens is used to concentrate the beam

Reflected back from the disc surface, on to the photo-diode array.

This lens is mainly used to improve the sensitivity of the photo diode array.

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Cylindrical lens

It is used to enable the reflected beam from the

Cd

to assist in creating the necessary signal to make sure

that that

focus of the laser beam on the playing surface of the disc is maintained.

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Drive motors in CD player

Types of drive motors used in CD player

Tray or loading motor

Disc, spindle or turntable motor

Slid , sled and feed motor

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Tray or loading Motor

It is also called carriage motor, moves tray in and

out for loading and unloading the disc.

Usually plastic tray is driven by a plastic gear box next to the play assembly.

The tray of loading motor is controlled by a loading driver IC and a signal from the system control IC processor.

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Slide, sled , feed motor

It moves the optical pick- up assembly across the disc from the inside to the outside rim of the CD , keeping the objective lens constantly in line with the centre of the optical axis or track.

The motor is gear driven to a rotating gear that moves pick-up assembly up and down.

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Spindle disc and turntable motor

The spindle motor starts to rotate after the disc has been loaded.

the disc starts

at approximately 500 RPM slows down to approximately 200RPM.

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Hi-Fi Amplifier

Hi-

Fi

means High Fidelity.

Fidelity means faithfulness.

High fidelity reproduction is essentially sound reproduction such that the most critical person can listen without any distortion.

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Hi-Fi

Amplifier Characteristics

Stereo Amplifier becomes Hi-

Fi

amplifier if the following requirements fulfilled-

1.Signal to noise ratio should be better than 50dB.

2.Frequency response should be flat within +-1dB.

3.The system should posses dynamic range of atleast 8dB.

4.Non linear distortion should be less than 1%.

5.Stereophonic effect should be provided.6. Environmental conditions should be such as to eliminate the external noise in listening room.

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Specifications of Hi-Fi Amplifier

Gain: voltage gain= 20log

vo

/

vin

(dB)

Bandwidth

Impedance

Distortion

i) Frequency distortion ii) Phase Distortion iii) Amplitude distortion iv) Self oscillation distortion

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Comparison of stereo and Hi-Fi

amplifier

Sr.No

Stereo Amplifier

Hi-

Fi

Amplifier

1

Less signal to noise ratio.

Better signal to noise ratio.2Non-linear distortion occurs.Non-linear distortion not more than input/output.3Equalizers not used.Equalizers used.4Two- way cross-over network with gain control exist.

Three- way cross-over network exist.

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Block diagram of Hi-Fi amplifier

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Block diagram of Hi-Fi amplifier

Left channel

Matching

ckt

.

Right channel

Pre-

Amplifier

Pre amplifierEqualizer

Equalizer

Power amplifier

Matching circuit

Power Amplifier

Matching Network

L.S.

L.S.

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Controls available on Hi-Fi

Aplifier

Balance , Blend and master gain control

Loudness control

Tone control

i)Bass control

ii) treble control

4.Quasi stereo switch

5.

Mic in6. Aux in7.Earphone in

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Block diagram of MP3 Player

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Block diagram of Flash MP3 Player

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A Home theater