What’s Available?
To further enhance realism, two 5.1-channel digital surround formats – Dolby Digital 5.1 and DTS Digital Surround – arrived on the scene in the 1990s. In consumer products, Dolby Digital decoders appeared in 1995 after inventor Dolby Labs (www.dolby.com) introduced the technology to the movie theater and film industries. Consumer products equipped with DTS, developed by Digital Theater Systems, soon followed (www.dtsdigitalsurround.com). Today, both formats appear on many DVD discs. Dolby Digital 5.1 also is delivered by digital cable operators, satellite systems and local digital TV (DTV) stations.

Dolby Digital and DTS deliver five discrete (fully separate) channels of full-range (20 Hz-20 KHz) audio to ramp up the realism and drama, while a separate low-frequency-effects channel (the 0.1 in 5.1) delivers the deepest bone-crunching bass. The effects channel can be delivered by a dedicated subwoofer or diverted to a system’s five full-range speakers.

Dolby Surround, in contrast, delivers a four-channel “matrixed” surround experience. A Dolby Surround mix tucks center-channel information and a limited-bandwidth (100 KHz-7 KHz) mono surround channel into two full-bandwidth stereo left-right channels. A Dolby Surround decoder extracts the hidden channels to deliver dialog to a center-channel speaker. The surround channel is split between two surround speakers.

Compared to Dolby Surround, 5.1-channel surround delivers effects with greater depth, localization and realism, in large part by bringing full-range stereo to the surround speakers. You can follow the sound of a jet flying over your head or a rocket-propelled grenade hissing past your shoulder.

Other 5.1-channel benefits include greater channel separation to deliver unprecedented spatial imaging, improved dialog intelligibility, enhanced resolution and greater dynamic range.

By August 2004, consumers bought 40 million Dolby Digital-equipped home theaters products, Dolby Laboratories said.

Some of the benefits of 5.1-channel surround now are coming to analog TV viewers. In 2001, the first home audio products equipped with Dolby Pro Logic II decoders hit the market to extract a five-channel-like surround experience from stereo and matrixed-surround sources, including content delivered by analog-TV stations and analog-cable systems. That format also works its magic on stereo CDs, FM stereo broadcasts and satellite-radio broadcasts – as does the rival SRS Circle Surround 5.1 format.

The effect is impressive, but when Pro Logic II and Circle Surround II decoders detect content encoded in either format, the surround experience achieves a higher level of realism and approximates the Dolby Digital 5.1-channel mixes available to DTV viewers. Circle Surround II decoders can also deliver a 6.1-channel experience through home theater systems that feature one or two back-center channels behind the listener.

Like Dolby Surround, the two technologies are matrixed technologies. They “fold” center-channel, left-surround and right-surround information into the two main stereo channels. As a result, any cable operator or TV station that broadcasts stereo can deliver content encoded in Dolby Pro Logic II or Circle Surround 5.1.

In 2004, analog cable operators and local analog TV stations delivered a growing amount of Pro Logic II and Circle Surround 5.1 content, having aired the first matrixed five-channel programs on a trial basis in 2002. In 2003, encoded content included the Country Music Awards, The Emmy’s, pro football games, other sporting events, select prime-time series, and even some commercials. During the 2004-2005 TV seasons, at least 17 regular programs and series were delivered in Pro Logic II through the ABC, NBC, PBS, Fox, HBO and USA networks, according to Dolby Laboratories.

For its part, NBC began in the 2004-2005 season to deliver Dolby Pro Logic II soundtracks to its analog TV affiliates. NBC also transports the signal to its DTV affiliates that broadcast in stereo and aren’t equipped to deliver Dolby Digital 5.1.

The installed base of home theater systems capable of decoding the signal grew to 15 million as of August 2004, Dolby Labs said.

For its part, Circle Sound inventor SRS Labs said 19 analog and digital TV broadcasters – from ABC to TNT – are delivering, or have delivered, select content in its matrixed 5.1-channel format. Select HD programs have also been delivered in the Circle Surround format, the company added.   

Hollywood’s High 5.1
Given the advantages of 5.1 discrete channels, the creative community has focused on using the “pure” 5.1 formats to mix video soundtracks, which have appeared on thousands of U.S. theatrical releases.

In turn, the movies’ 5.1-channel soundtracks are turning up on a growing number of DVDs. In the U.S., the number of 5.1-channel U.S.-market titles grew to 10,200 in February 2005 out of 46,000 titles available, according to Muze (www.muze.com), which compiles databases of entertainment product information for retailers. In February 2000, fewer than 1,000 titles were available with 5.1 soundtracks, according to DEG.

For households lacking 5.1 decoders, Hollywood backs up its 5.1-channel DVD soundtracks with stereo or Dolby Surround.