Dolby Digital is often referred to as a 5.1 channel system. However, it must be noted that term "Dolby Digital" refers to the digital encoding of the audio signal, not how many channels it has. In other words, Dolby Digital can be Monophonic, 2-channel, 4-channel, 5.1 channels, or 6.1 channels. However, in its most common applications, Dolby Digital 5.1 and 6.1 is often referred to as just Dolby Digital.
The Benefits Of Dolby Digital 5.1
Dolby Digital 5.1 adds both accuracy and flexibility by adding stereo rear surround channels that enable sounds to emanate in more directions, as well as a dedicated Subwoofer Channel to provide more emphasis for low frequency effects.
Also, unlike Dolby Pro-logic which requires a rear channel of only minimal power and limited frequency response, Dolby Digital encoding/decoding requires the same power output and frequency range as the main channels.
Dolby Digital encoding on DVDs, Laserdiscs, and Satellite programming is very common and has solidified this format in the marketplace. Since Dolby Digital involves its own encoding process, you need to have a Dolby Digital receiver or amplifier to accurately decode the signal, which is transferred from a component, such as a DVD player, via either a digital optical connector or digital coaxial connector.
Dolby Digital EX is actually based on the technology already developed for Dolby Digital 5.1. This process adds a third surround channel that is placed directly behind the listener.
In other words, the listener has both a front center channel and, with Dolby Digital EX, a rear center channel. If you are losing count, the channels are labeled: Left Front, Center, Right Front, Surround Left, Surround Right, Subwoofer, with a Surround Back Center (6.1) or Surround Back Left and Surround Back Right (which would actually be a single channel - in terms of Dolby Digital EX decoding). This obviously requires another amplifier and a special decoder in the A/V Surround Receiver.
The Benefits Of Dolby Digital EX
So, what is the benefit of the EX enhancement to Dolby Digital Surround Sound?
Essentially, it boils down to this: In Dolby Digital, much of the surround sound effects move towards the listener from the front or sides. However, the sound loses some directionality as it moves along the sides to the rear, making a precise directional sense of sounds from moving objects moving or panning across the room difficult. By placing a new channel directly behind the listener, panning and positioning of sounds emanating from the sides to the rear are much more precise. Also, with the additional rear channel, it is possible to originate sounds and effects from the rear more precisely as well. This places the listener even more in the center of the action.
Dolby Digital EX Compatibility
Dolby Digital EX is completely compatible with Dolby Digital 5.1. Since the Surround EX signals are matrixed within the Dolby Digital 5.1 signal, software titles encoded with EX can still be played on existing DVD players with Dolby Digital outputs and decoded in 5.1 on existing Dolby Digital Receivers.
Although you may end up buying new EX-encoded versions of films you may have already in your collection when you finally get your EX setup running, you can still play your current DVDs through a 6.1 Channel Receiver and you will be able to play your new EX-encoded discs through a 5.1 channel receiver, which will just retain the additional information with the current 5.1 surround scheme.
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