Receivers go by many names: multimedia receivers, car stereos and head units. No matter the name, the receiver is possibly the most important piece of any audio system. Sure, you won't get much sound without speakers, but it's the stereo that gives you control over music and radio, equalizer settings to tweak how your system sounds, and a way to interface with data on CDs, cassettes, smart phones, MP3 players or DVDs.
Receivers typically include displays to show you what your audio system is currently playing and buttons for switching inputs and presets. Car stereos adhere to certain sizes, which makes them easy to upgrade. If you're still using a plain ol' CD head unit in a 2003 Corolla, for instance, consider upgrading to a model with a multi-disc changer and a USB port for connecting to an iPod. Some receivers are compatible with satellite radio, which is a must if you're interested in Sirius XM. Of course, if you want a multimedia receiver with wireless capabilities, get a Bluetooth car stereo.
The head unit is the brain center of your audio system; make sure it enables all the functionality you're looking for. Next we'll take a look at an even more advanced system often embedded in car dashboards: GPS.