Sound Reproduction (Part 4 : Compact disc )

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Ideally, sound reproduction equipment recreates the sound exactly as originally

recorded. An amplifier must boost the level of the electric signal from the record ,

tape, or CD player without introducing unpleasant distortion. Most amplifiers

accomplish this using transistors, but amplifiers based on older vacuum tube

technology are prized by some for the "warmth: of their sound. The final

component in the reproduction chain is the loudspeaker. Speakers are transducers.

They convert electric energy into sound energy, and work like microphone in reverse.

Most speakers use moving-coil technology. "Flat" speaker designs were once usually

based on electrostatic technology and operated like condensor microphones in reverse,

but the latest flat designs use a new "distributed mode" speaker technology.

Compact disc :

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The compact disc is a 5 in. (12 cam) diameter plastic disk that can hold

approximately 74 minutes of 16-bit stereo sound, sampled at 44.1 kHz. The sound data is

stored in the form of about 3 billion "pits: in a single spiral track that starts at the center.

A typical pit is 1/40,000 in (1 micrometer) long.

CD player :

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Information is stored on a CD as a series of pits. Pits and lands (the areas in

between) represent the digital sound data. In the player, a laser beam is focused on the

track from beneath the disc and reflected back to a detector. The varying intensity of this

light (caused by the pattern of pits and bumps) is converted into an audio signal.

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