Digital Television is capable of bringing Digital Surround Sound into your home. Before Digital, the most advanced form of surround sound that could be broadcast is Dolby Pro-Logic.
What is Surround Sound?
Most people are probably aware that you can get "high-end" televisions and VCRs which can deliver Hi-Fi Stereo sound. These are most commonly connected to Hi-Fi audio equipment for maximum benefit. This can significantly increase the quality of TV sound, but it still is nothing like the "cinema experience".
In cinemas, most new films use "Dolby Digital" sound... a format which provides five individual sound channels (Front Left, Front Centre, Front Right, "Surround" Left and "Surround" Right). The Surround channels are delivered through the speakers mounted along the side walls of the cinema. In addition, Dolby Digital provides a low-frequency sound channel which isused for deep bass effects. This form of surround sound is sometimes known as 5.1 channel surround.
There are more advanced standards now around for cinema audio - but I'll stick to discussing what will be available on Digital Television.
Most Hollywood films since the 70's have used some form of surround encoding, with Front Left, Front Centre, Front Right and "Surround" channels.
Surround Sound at Home
There have been several forms of Surround Sound available in the home. The most popular over the years has been Dolby Pro-Logic. This format can produce four sound channels (Front Left, Front Centre, Front Right and Surround). These can be encoded into two sound channels... which is conveniently the number available in Hi-Fi Stereo broadcasts and video cassettes.
Most movies that you can rent or buy will carry Dolby Surround encoding, often even if it isn't mentioned on the box. Similarly, most movies shown on TV will carry it as well as a handful of other programs and the odd commercial. Again, some are marked, some aren't.
Dolby Pro-Logic has its problems, especially in the broadcast environment. The decoded channels are never as clearly separated on a broadcast as they are on a video cassette. True audio junkies will also complain that the four channels aren't really full channels either.
DSP (Digital Signal Processing) Surround should not be confused with surround sound! This is a form of digital processing which looks at a Mono or Stereo audio source and attempts to make surround sound out of it. It will have nothing to do with the carefully mixed surround sound encoded into some stereo audio sources. If your equipment doesn't say Dolby Surround Pro-Logic on the casing... then it isn't.
Digital 5.1 Channel Surround Sound at Home
Enter Digital Surround. Easily the most popular digital surround format in the market today is Dolby Digital AC-3. It provides the 5 full-frequency channels and 1 low-frequency channel that you get in a cinema. It provides it in a digital format.
It should be noted however... there is also an MPEG 5.1 channel digital sound format. This format has its supporters and detractors. The biggest problem I find gaining information is that most people who should know about it have invested in Dolby AC-3 equipment. Go figure.
Dolby AC-3 has also been around longer, so there is far more information available on the web about it than the MPEG variety.
Surround Sound and DVB-T
Australia was the driving force behind Surround Sound being seriously incorporated into DVB-T. It did have provision for MPEG 5.1 Surround - but we were logically more interested in the already-successful Dolby Digital. Provision was made in the DVB-T standard for this to be allowed and it has since been adopted elsewhere as well.
Unfortunatly now Australian broadcasts may feature Dolby Digital or MPEG Musicam Stereo - or both. It was a misguided attempt to reduce the cost of set top boxes, but those who made the decision did not understand that it actually does not make any material difference.
© Digital Television News Australia 1998-2009