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' The brains and nerve center of your system.

Receivers perform many different important functions in your system. Along with being the central audio and video switching station, they handle audio signal processing and amplification, radio tuning, and, in some high-end models, upconversion of standard video signals for high-def output through Component Video or HDMI jacks. Other features you'll find on receivers include ports for connecting an XM satellite radio antenna or iPod. Since the receiver is such a key component, it's important to do your homework and select one that provides enough input and output connections to accommodate all your audio and video sources.

' Stereo, 5.1, 6.1, and 7.1-channel receivers explained

Any receiver can handle two-channel stereo playback, but a basic model should also come equipped with Dolby Digital and, in most cases, DTS surround sound processing - an alternative digital soundtrack format that's found on some DVDs. Both of these formats use five discrete audio channels plus a special low frequency (bass) effects channel to deliver immersive, near-movie theater quality sound from DVDs or high-definition sources. Most step-up receivers add on Dolby Digital EX and DTS-ES processing. These modes make use of an additional "back" surround channel to extend the sonic possibilities of Dolby Digital and DTS even further.

'The most common type of receiver -5.1-channel models- decode the audio information contained in Dolby Digital and DTS soundtracks and route them to front left and right, center, and surround speakers in your system via their five built-in amplifier channels. (The .1, or low frequency effects, channel in a movie soundtrack gets directed to a powered subwoofer with its own on-board amplifier.)

'Along with providing all the functionality of a 5.1-channel receiver, 6.1-channel models include an additional amp channel to drive a back surround speaker when watching DVDs encoded with Dolby Digital EX or DTS-ES soundtracks. The main benefit to the back surround channel is that it creates an even more realistic surround sound experience - one that's closer to what you'd hear in a well-equipped movie theater.

'7.1-channel receivers are basically the same as 6.1-channel models, but they include yet another amp channel to drive a second back surround speaker. In this case, the audio information going to both back speakers is identical; it's just distributed between the two back speakers to create an even more expansive rear sound field. The specifications for the new HD DVD and Blu-ray disc formats allow for soundtracks with up to 7.1 discrete audio channels. So while a 7.1-channel receiver might seem like overkill, right now it's a more future-proof option than 5.1 and 6.1 models.

' Audio formats - Dolby Digital, DTS, THX, and Dolby Headphone explained

As discussed in Stereo, 5.1, 6.1, and 7.1 surround sound explained, Dolby Digital and Dolby Digital EX, and DTS and DTS-ES are the main surround sound audio modes you'll find on both basic and step-up receivers. But higher-end models may offer even more processing modes. For example, THX-certified receivers feature something called THX Surround EX. This mode works alongside Dolby Digital EX processing to time-align a pair of back surround speakers in a 7.1-channel system and match their sound to the other speakers in the system. The end result is a more seamless, theater-like surround presentation when watching DVDs with Dolby Digital EX-encoded soundtracks. And then there's Dolby Headphone, a processing mode that brings the dynamic range, dialog clarity, and spatial effects of 5.1-channel Dolby Digital soundtracks to stereo headphone listening. Although using headphones in a fully equipped home theater might sound strange, it's a great option for late-night viewing when you don't want to disturb others in the house.

' Basic receiver setup.

Basic receiver setup entails plugging in audio and video sources and running wire from the unit's back panel to your speaker's input connections. Most DVD players, CD changers, satellite receivers, and cable boxes provide a digital audio output along with a set of regular analog output jacks. You'll usually get better sound if you use this digital audio connection, and it's an absolute requirement to experience the 5.1-channel digital soundtracks on DVDs or HDTV programs. The rules for video setup on receivers are pretty much the same as those for audio. If your video source has a digital DVI or HDMI connection (and the receiver provides digital video switching) it will deliver better performance than analog Component Video, Composite and S-Video connections.

'Speakers.

The sound coming from your receiver needs to be divided up to match the capabilities of the speakers used in the system. To do this effectively, a receiver's speaker setup menu lets you specify the size of individual speakers in the system as large or small, and asks whether or not you're using a subwoofer. The settings you select allow it to perform bass management, which determines the precise audio frequency at which bass signals are filtered out from the various speakers and sent on to the subwoofer (or to the main speakers, if a subwoofer isn't used). The next step is to measure the span from the speakers to your seating position and specify those distances in the setup menu. This allows the receiver to perform time-alignment - basically adding slight delay to the audio channels to create a more uniform surround sound effect. And the final setup task is to balance the output levels of each speaker in the system. This ensures that the sound coming from all speakers is equally loud - an important step for getting smooth dialog and realistic surround ambience. Some receivers perform the task automatically; with others, you need to use a sound-pressure level meter along with the receiver's built-in setup test tones to manually make the adjustments.

' How many watts per Channel?

The amount of power you'll need from a receiver depends on two factors: room size, as well as the performance characteristics of the speakers you're pairing it with. An average power rating for a receiver is 100 watts per channel. That level of juice should be enough for a small to mid-size (80 to 200 square foot) home theater with a five satellite-plus-subwoofer speaker system. But large tower speakers - particularly those that use exotic technologies like planar-magnetic or electrostatic drivers - might require more amplifier power to handle the sonic peaks in an action movie than a 100 watt-per -channel receiver can provide.

' Get the most out of your receiver and system

Since a receiver is the brain of your system, you should try to maximize its features to make your life easier and more enjoyable. At minimum, you'll want to take advantage of its tape loop functions to route signals to a CD- or DVD-recorder or VCR for basic audio and video recording. Many higher-end models also provide a multizone audio output that lets you direct stereo music or radio programs to a secondary room such as a dining area or kitchen.

'Room Auto-EQ systems

A new feature found on some receivers is automatic equalization, or Auto-EQ. While this feature varies from receiver to receiver, it's typically used to improve sound quality by automatically adjusting parameters such as speaker crossover points. Auto-EQ can also adjust the bass and treble of individual audio channels to compensate for any issues with room acoustics. Receivers with Auto -EQ usually come with a small microphone that's used for initial setup. The receiver emits test tones from each speaker in sequence, while the microphone picks up the tones and provides feedback. This information is then used to automatically adjust speaker levels, speaker distance settings, and various EQ and room-correction functions.

'Receiver or separate preamp/processor and amplifier

Buying a receiver with all its bundled extras is hands down the easiest way to get started when putting together a home theater. But there are also downsides to this approach. Stuffing numerous electronic components like a preamp/processor, multichannel amp, and radio tuner together in a single chassis can increase background noise levels -which is why audio purists prefer to buy those components separately. With new home theater innovations arriving at a lightning-fast pace, buying separate components also gives you insurance against obsolescence - you can upgrade your preamp/processor without having to buy a new amplifier, and vice-versa.