5.1 digital sound is the high-end audio complement to high definition television and many audio post facilities are ready to provide spot clients with its inherent six distinct sound channels.While the format provides new heights of aural pleasure, it also means challenges for those facilities making the investment to meet the current 5.1 demand, which comes largely from cinema spots, since digital television has hardly saturated the consumer market, and the era of full-blown high definition TV commercial production has yet to arrive. The multitude of existing audio formats further complicates the situation.

Audio facilities in all markets have geared up for 5.1, including Santa Monica's POP Sound, Toronto's Manta Eastern Sound, New York's Cool Beans and Atlanta's Crawford Communications, which made a large investment in the format with its new facility (see story pg. 59).

5.1 digital sound (most commonly formatted to Dolby standards) is a leg up from Dolby Surround, its predecessor. Most TV signals are currently broadcast in stereo with two channels of sound; left and right. Dolby Surround Sound, the standard commonly used for VHS cassettes, is an analog, encoded, 2 channel signal that, when played through a decoder, provides four channels of listening pleasure; left, center right, and a mono surround channel that is not a full bandwidth signal. This means that the surround channel does not reproduce the full range of audio we are capable of hearing.

The 5.1 system provides real, digital six-channel surround sound, with left, center and right channels, as well as distinct left surround and right surround signals, which are full bandwidth. In addition to these five signals is the .1, a low frequency subwoofer signal. This means sound effects, voices and background music can be more animated and precisely located. For example, an on-screen gunshot or jet flying overhead could feature sound effects panning from speaker to speaker within the surround channels, creating more movement than is possible in Dolby Surround. In addition to more movement is increased clarity, especially apparent in the surround channels, due to the fact that Dolby 5.1 is a full bandwidth digital signal, while Dolby surround is analog.

Loren Silber, a mixer at POP Sound in Santa Monica, CA explains why this sort of signal is technically superior to basic Surround Sound.

"Dolby 5.1 is not encoded, it is a discrete system, meaning it will provide six channels of audio," says Silber, comparing the newer format with the older encoded signal. "The process of encoding or decoding and keeping the signal compatible for stereo (which should be done for broadcast) means you can't put too much sound in the back speakers, or it won't show up when you play it back in mono."

Silber works on an AMS Neve Audiofile with a Logic 2 digital console, capable of working in the 5.1 format. Silber cautions that even though Dolby 5.1 allows for better sound quality, it isn't readily usable for the vast majority of TV commercials. "5.1 isn't able to be broadcast in the way we broadcast now. It requires a whole new broadcast standard," says Silber. "Dolby 5.1 sacrifices compatibility with the current broadcast standards for quality of sound!"