AV receiver

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AV receivers or audio-video receivers are one of the many consumer electronics components typically found within a home theatre system. Their primary purpose is to amplify sound from a multitude of possible audio sources as well as route video signals to your TV from various sources. The user may program and configure a unit to take inputs from devices such as DVD players, VCRs etc. and easily select which source you want to route to your TV and have sound output for.

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[edit] Usage

The term receiver originally referred to a component which included a tuner, a pre-amplifier and a power amplifier. These receivers were sometimes called stereos. The modern AV receiver provides for these functions, but extends the amplification to more than two channels. The modern AV receiver usually provides at least one multi-channel decoder and usually provides for audio as well as video switching. It may also provide for video processing such as up conversion, deinterlacing and scaling. Some have networking capabilities and can play music from the Internet, or music stored on a computer or media server.

[edit] Features

[edit] Radio reception

Receivers usually have a built in tuner for Amplitude Modulation (AM) and Frequency Modulation (FM) radio reception. Satellite radio tuners are also found in many modern receivers, allowing reception with just an external antenna (and a satellite radio subscription, if necessary). Future models may drop radio features of all kinds in favor of support for MP3 players, and the normally used devices such as CD players, turntables, etc. as it may cut the cost of the devices.

[edit] Decoders

AV receivers usually provide one or more decoders for sources with more than two channels of audio information. This is most common with movie soundtracks. Movie soundtracks have been provided via a number of encoded formats. The first common format was Dolby Pro Logic. This format contained a center channel and surround channel. These channels were mixed into the left and right channels using a process called matrixing. Receivers were produced with Dolby Pro Logic decoders which could separate out these two additional channels.

With the introduction of the DVD, the Dolby Digital format became a standard. Dolby Digital ready receivers included inputs and amplifiers for the additional channels. Most current AV receivers provide a Dolby Digital decoder and at least one digital S/PDIF input which can be connected to a source which provides a Dolby Digital output.

A less common format called DTS is present on some DVDs. Many newer AV receivers provide this decoder as well.

A number of other decoders may be provided by the AV receiver such as Dolby Digital EX, Dolby Pro Logic IIx, DTS Digital Surround, DTS-ES, DTS 96/24, and DTS Neo:6.

[edit] DSP effects

Most receivers offer specialized Digital Signal Processors (DSP) made for handling various presets and audio effects. Some may offer simple equalizers and balance adjustments to complex DSP audio field simulations such as "Hall", "Arena", "Opera", etc. that simulate the audio being played in the places through use of surround sound and echo effects.

[edit] Amplification

Stereo receivers have two channel of amplification, while AV receivers have at least 2 channels. The standard for AV receivers is five channels of amplification. These are usually referred to as 5.1 receivers. This provides for a left, right, center, left surround and right surround speaker to be powered by the receiver. 7.1 receivers provide for two additional surround channels, left rear surround, and right rear surround. The '.1' refers to the LFE (low frequency effects) channel the signal of which is usually sent to an amplified subwoofer unit. 5.1 and 7.1 receivers don't usually provide amplification for this channel. Instead, they provide a line level output.

There are various standards for rating the output power of receivers. Different countries have different rules on how manufacturers specify the output ratings. Its not always possible to use these ratings to compare two products. Due to a number of factors such as real world behavior of speakers and dynamic headroom its possible for an amplifier with a lower rated power to play more loudly than one with a higher rated power.

Differences in output power are not always as significant as they may look. It takes 10 times the output power for the sound to be perceived as twice as loud. If 1 watt of output yields a sound pressure level of 90dB, it takes 10 watts to get an SPL of 100dB and 100 watts to get an SPL of 110dB. A 110 watt amplifier will not play 10% louder than a 100 watt amplifier.

Most receivers use class AB amplifiers. Some manufacturers are now producing receivers using class D amplifiers. Class D amplifiers are more efficient and can be made smaller and lighter than an equivalent class AB amplifier. There are also other designs such as class G and class H. Class G and H are variations on the conventional class AB design. Class G has two sets of power supply rails. Normally the power amp is fed from the lower voltage supply. This helps keep power dissipation in the output transistors down. When the signal exceeds the lower supply voltage, the amp switches to the higher voltage supply so the signal can be reproduced without clipping. With a class H design, the supply rails are variable rather than two discrete steps. The signal actually modulates the supply voltage.

[edit] AV Inputs/Outputs

There are a variety of possible connections on an AV receiver. Some common connectors include:

Analog audio connections usually use RCA plugs in stereo pairs. Inputs and outputs are both common. Outputs are provided mainly for cassette tape decks.

Analog audio connections using XLR connectors are uncommon, and usually found on more expensive receivers.

Digital connections allow for the transmission of PCM, Dolby Digital or DTS audio. Common devices include CD players, DVD players, or satellite receivers.

Composite video connections use a single RCA plug on each end. Composite video is standard on all AV receivers allowing for the switching of video devices such as VHS players, cable boxes, and game consoles. DVD players may be connected via composite video connectors although a higher bandwidth connection is recommended.

S-Video connections offer better quality than composite video. They use a DIN jack.

Scart connection offers better quality than S-Video cable, but worse than Component Video. Scart connection provides video and audio in one connection

Component video is the best connection for analog video.

HDMI connections are becoming common on AV receivers. It provides for the transmission of both audio and video. HDMI is relatively new technology and there are reported issues with devices not properly working with each other, especially cable/satellite boxes connected to a display through an AV receiver. Different levels of support are provided by receivers with HDMI connections. Some will only switch video and not provide for audio processing. Some will not handle multi-channel LPCM. Multi-channel LPCM is a common way for Blu-ray and HD DVD players to transmit the best possible audio.

[edit] Video conversion and upscaling

Some receivers can convert from one video format to another. This is commonly called upconversion or transcoding. A smaller number of receivers provide for de-interlacing of video signals. For example, a receiver with upconversion, deinterlacing and upscaling can take an interlaced composite signal at 480i (480 lines per frame sent as a field of 240 even numbered lines 0,2,4,8...478 followed by a field of 240 odd numbered lines 1,3,5,...479) and convert it to component video while also deinterlacing and upscaling it to a higher resolution such as 720p (720 lines per frame with all lines in normal sequence 0,1,2...719).

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