A Surround Sound Receiver usually combines the functions of three components:
1. A radio tuner for AM/FM and, in some cases, HD (High Definition Radio) or XM-Satellite Radio.
2. A Preamplifier that switches and controls which audio and video source is selected (such as a DVD player, VCR, CD player, etc...) and processes the incoming stereo or surround sound signals and distributes them to the correct amplifier channels and the subwoofer output. The preamp in a surround sound receiver can also route video signals coming from source components (such as a DVD player) and direct the video signal to the television.
3. A built-in Multi-channel amplifier (5.1, 6.1, or 7.1 channels) that sends the surround sound signals and power to the speaker system.
