Handbook for Sound Engineers

Surround Sound 1595

matrixing, wider dynamic range, and what became

known as the 5.1-channel configuration.

As shown in Fig. 45-3, the 5.1 configuration

provides fully discrete left, center, right, left surround,

and Right Surround channels. A sixth channel, intended

for reproduction by subwoofers, carries low-frequency

effects (LFE), and became known as a .1 channel

because it covers only a tenth of the audible spectrum.

5.1 has its roots in the 70 mm six-track magnetic

format. Originally the six-track configuration called for

five full-range screen channels and one surround

channel. As the average cinema screen became smaller

in the 1970s, however, the need for five full-range

screen channels and elaborately panned dialogue less-

ened. Dolby therefore proposed that the extra two

screen loudspeakers, often referred to as half-left and

half-right, could be used more effectively for bass rein-

forcement, with the correlating tracks on the film

carrying only bass information, as shown in Fig. 45-1.

This technique, which was adopted by the industry and

earned the nickname “baby boom,” was the precursor of

the .1 channel and its attendant subwoofers in today’s

digital formats.

The use of two surround channels was also a 70 mm

contribution, beginning with some experimental 70 mm

prints of the film Superman in 1978. What the industry

came to call stereo or split surrounds was first heard by

the public late in 1979 in fifteen specially equipped

theaters showing 70 mm prints of Apocalypse Now.

The first 5.1-channel digital format was cinema

digital sound (CDS), introduced in 1990 by Optical

Radiation Corp. and developed in conjunction with

Kodak. The CDS format placed a digital optical sound-

track on 70 mm prints in lieu of analog magnetic tracks,

and experiments with 35 mm prints were underway

when the venture failed. Soon thereafter, beginning in

1992, came the three competing 35 mm digital film

sound formats that have survived with varying degrees

of success: Dolby Digital, Digital Theater Sound (DTS),

and Sony Dynamic Digital Sound (SDDS).

The three digital formats differ more in how they

deliver their respective digital soundtracks than in their

actual performance. Both Dolby and SDDS use optical

digital soundtracks on the print, the Dolby Digital track

between the sprocket holes down one side, and redun-

dant SDDS tracks down both outer edges. DTS supplies

the digital soundtrack separately on a CD-ROM disk

that plays in sync with the picture by means of an

optical time-code track adjacent to the analog sound-

track on the film. To insure playback in any theater,

many release prints provide for all three digital formats

plus analog playback, giving rise to the nickname quad

print, Fig. 45-4.

45.4 Variations on the 5.1 Theme

While the 5.1 configuration became the de facto stan-

dard for multichannel digital film sound in the cinema

(and for the home as well, as will be seen), both Dolby

and SDDS offered producers the option of using addi-

tional channels. With SDDS, it is possible to mix for a

total of seven main channels, bringing back the

full-range half-left and half-right screen channels of the

original 70 mm magnetic format. Thus far relatively

few films have been so mixed, and relatively few the-

aters are equipped with the extra full-range screen loud-

speakers required.

The Dolby option, called Dolby Digital Surround

EX, was co-developed with Lucasfilm THX, and has

achieved some success since its introduction in May of

1999 with the release of Star Wars: Episode I–The

Phantom Menace. Surround EX offers the option of a

third surround channel intended for reproduction by

rear-wall surround loudspeakers, while the left and right

surround channels are reproduced by the side-wall

surrounds.

Not a discrete track, which is why the format’s

co-developers originally avoided the term 6.1, the extra

surround information is matrix-encoded onto the left

and right surround channels of otherwise standard. 5.1

soundtracks. This insures print compatibility with

Figure 45-3. To insure compatibility with all theaters,
35 mm quad prints feature three digital soundtracks plus
an analog SR track.

Dolby Digital

Dolby SR analog

DTS timecode*

Primary SDDS Redundant

*DTS soundtrack is on a CD-ROM

which syncs to the film via timecode