Audio systems need speakers and a source of sound, such as a DVD, video game or CD. To hear the source, it must be amplified, then customized with bass, treble, etc.

In today's home theaters this important job is left to the receiver. It acts as the "brain," accepting signals from various sources, processing the sound and outputting it to speakers so you can enjoy movie soundtracks, games, music and more.

Thankfully, these complex products, whether for stereo or surround sound playback, are easy to set up and use, and they can really add a lot of enjoyment to your life.

There are a lot of receivers to choose from, so it's important to understand the various features and functions that make some models more expensive than others. Here are some things to look for when shopping:

Surround sound: Unless you're only going to listen to CDs and your old record collection, it makes sense to invest in a model that has Dolby Digital and DTS sound. With one, you can enjoy DVD movies in theater-like surround sound, along with new high-resolution, surround sound music formats SACD and DVD-Audio.

Optical/coaxial digital inputs: If you choose a surround sound receiver, make sure you have enough of these. In addition to DVD players, you'll need additional inputs to get surround sound from PS2, Xbox, and many digital cable and DIRECTV receivers.

Component video: Get a receiver with these inputs and outputs if you already own or plan to own a digital TV. You can use your receiver as an extra set of high-definition inputs for a progressive-scan DVD player or HD receiver.

Discrete circuitry: Separate transistors, resistors, diodes rather than integrated circuit chips. Sound quality will be much better on these models-don't be dissuaded by the lower wattage numbers.

Large filter capacitors: Capacitors store energy, which can be then used to fully capture musical peaks.

Large power transformers and high current capability: Translates into better performance at all frequencies as loudspeaker impedance changes and allows greater dynamic range without distortion.

Wide power bandwidth: Although we can't hear more than 20-20,000Hz, an amp that can go beyond this is a good thing. Just as you want a car that can go more than 65mph, you want an amp with wide bandwidth.

This information is a good head start. Use it to get started and be sure to stop into your local Circuit City store to get answers to any questions you might have about all the great things a receiver can do for your home theater.