Home Cinema Guide:
The various surround sound formats available on modern AV receivers can appear confusing. Dolby Digital, DTS and THX listening modes are all available to process your audio, but what is the difference and what do they all do?
After purchasing a new audio/video receiver I wanted to better understand the different sound settings available. This site provides a great summary of the basics. It would have been helpful if it also explained the term PCM. It stands for pulse-code modulation, and it is simply a 2-channel stereo signal that most electronic devices default to when they don’t have a true surround (i.e. 5.1 channel) signal.
For a briefer summary, take a look at the Surround Sound Format Chart put together by Crutchfield.