What Does 7.1 and 5.1 Surround Sound Actually Mean?

THE DIFFERENCE BETWEEN 5.1 AND 7.1 SURROUND SOUND
The most common surround-sound home theater systems contain 5.1 surround digital receivers from such manufacturers like Sony, Yamaha and Denon. Dolby Laboratories actually invented surround sound back in the 1980's and manufacturers have to pay a licensing agreement to Dolby if they want to embed 5.1 or 7.1 Dolby Digital sound into their own receivers.
The reason for the different number sequences is based on how many speakers it takes to reach the full surround mode of each sound system. For instance, you can get full 5.1 surround from your receiver as long as you have one subwoofer, one center speaker, two side speakers and two rear-channel speakers. The 'one' in this sequence is alluding to the subwoofer. But if you want true 7.1 surround, you must also include two more rear speakers directly behind the listener, such as the speakers you would find in a professional movie theater.
A TRUE MOVIE EXPERIENCE REQUIRES 7.1 DIGITAL SURROUND SOUND
Most Blu-ray and non-Blu-ray DVD movies are being encoded with 71 DTS-HD Master Audio these days, along with the usual 5.1 Dolby surround sound mode. This means that in order to experience the most realistic true movie theater audio signatures while watching a movie like 'Avatar', for instance, you really need to upgrade your 5.1 surround receiver fairly soon.
If you do own a 7.1 digital receiver that can decode and play a Blu-ray movie with DTS-HD Master Audio but the movies you own aren't equipped with that specific sound mode, don't worry. Your 7.1 digital receiver will still do a great job of perfectly balancing the typical 5.1 surround sound into all of your seven speakers contained with your home theater system.
5.1 SOUND CONVERTED OVER TO 7.1 SOUND WITH YOUR RECEIVER
When you do watch a 5.1 digitally encoded DVD movie on your current 7.1 digital receiver, your component will actually convert the 5.1 sound to all of seven of your speakers through something called 'duplicated sound processing.' This fancy term just means that your extra rear center channel speaker will duplicate the exact sounds emanating from your other two rear channel speakers, thereby creating a real professional movie theater experience.
To sum up, as long as your home theater receiver includes a variety of either 5.1 surround modes such as Pro Logic or Theater Surround, and your 7.1 digital receiver includes DTS-HD Master Audio, your home theater listening experience will be second to none