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In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and converts the signal into sound, pictures, navigational-position information, etc. Radio and radio receiver are often used specifically for receivers whose output consists only of sound, although other types of receivers, such as television receivers, are technically radio receivers as well.

A radio receiver is a real world example of a receiver in the information theoretic sense.



圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/6/68/Truetone-Radio.jpg/250px-Truetone-Radio.jpg



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
Old-fashioned radio receiver--wireless Truetone model from about 1940
As an audio appliance, "receiver" refers to a tuner, a preamplifier, and a power amplifier all on the same chassis. Audiophiles will refer to such a device as an integrated receiver, while a single chassis that implements only one of the three component functions is called a discrete component. Some audio purists still prefer three discreet units - tuner, preamplifier and power amplifier - but the integrated receiver has, for some years, been the mainstream choice for music listening. The first integrated stereo receiver was made by the Harman Kardon company, and came onto the market in 1958. It had undistinguished performance, but it represented a breakthrough to the "all in one" concept of a receiver, and rapidly improving designs gradually made the receiver the mainstay of the marketplace.

Most older receivers also came with a loudspeaker (see photo).



[edit] Hi-Fi / Home theater


Main article: Home cinema
Today AV receivers are a common component in a high-fidelity or home-theatre system. The receiver is generally the nerve centre of a sophisticated home-theatre system providing selectable inputs for a number of different audio components like turntables, compact-disc players and recorders, and tape decks ( like video-cassette recorders) and video components (DVD players, video-game systems, and televisions).

With the decline of vinyl discs, modern receivers tend to omit inputs for turntables, which have separate requirements of their own. All other common audio/visual components can use any of the identical line-level inputs on the receiver for playback, regardless of how they are marked (the "name" on each input is mostly for the convienience of the user.) For instance, a second CD player can be plugged into an "Aux" input, and will work the same as it will in the "CD" input jacks.

Some receivers can also provide signal processors to give a more realistic illusion of listening in a concert hall. Digital audio S/PDIF and USB connections are also common today.

Some modern integrated receivers can send audio out to seven loudspeakers and an additional channel for a subwoofer and often include connections for headphones. Receivers vary greatly in price, and support stereophonic or surround sound. A high-quality receiver for dedicated audio-only listening (two channel stereo) can be relatively inexpensive; excellent ones can be purchased for $300 US or less. Because modern receivers are purely electronic devices with no moving parts unlike electromechanical devices like turntables and cassette decks, they tend to offer many years of trouble-free service. In recent years, the home theater in a box has become common, which often integrates a surround-capable receiver with a DVD player. The user simply connects it to a television, perhaps other components, and a set of loudspeakers.

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