Three Formats Fought for Digital Cinema Sound Sound in Film

By 1990 analog optical sound had hit its ceiling

Dolby SR (Spectral Recording), introduced in 1986, pushed analog optical sound as far as it could go — roughly 78 dB of dynamic range with noise reduction engaged, and a frequency response extending to around 12 kHz. For comparison, a compact disc delivered 96 dB of dynamic range and flat response to 20 kHz. Audiences who owned CD players at home were increasingly hearing better audio fidelity in their living rooms than in theaters. Digital cinema sound was inevitable.

Three competing systems launched within eighteen months of each other, all aiming to put digital audio onto 35mm release prints without eliminating the existing analog track.

Dolby Digital debuted on Batman Returns in June 1992

Dolby's system — originally branded "Dolby SR-D" — encoded 5.1 channels of digital audio (left, center, right, left surround, right surround, and a low-frequency effects channel) as data blocks printed between the sprocket holes on the 35mm print. The data occupied physical space on the film that had previously been unused. The system delivered 20 Hz to 20 kHz response and over 90 dB of dynamic range per channel. Batman Returns was the first film released with Dolby Digital in June 1992. (wikipedia)

The codec used perceptual coding (AC-3) to compress six channels into a data rate of 320 kbps — lossy compression, but designed to be transparent to human hearing in a theatrical environment. The same AC-3 codec would later become the standard audio format for DVD.

DTS launched with Jurassic Park in June 1993

Digital Theater Systems took a different approach. Rather than encoding the digital audio on the film itself, DTS printed a timecode track on the 35mm print and stored the actual audio on separate CD-ROMs that played in synchronization with the projector. The CD-ROM approach allowed higher data rates (roughly 1.5 Mbps for a 5.1 mix) and less aggressive compression than Dolby Digital, which DTS marketed as a sound-quality advantage. Terry Beard, DTS's founder, demonstrated a remastering of Close Encounters of the Third Kind to Spielberg, who then selected DTS for Jurassic Park (1993) and became a financial backer of the company. With Universal/Matsushita backing, over 800 theaters adopted DTS by the June 1993 opening. (wikipedia)

The separate-disc approach had practical drawbacks — the CD-ROMs had to be shipped, loaded, and synchronized correctly by projectionists — but it worked, and the perceived quality advantage attracted a dedicated following among sound-conscious filmmakers and exhibitors.

SDDS arrived last and never caught on

Sony Dynamic Digital Sound (SDDS) encoded up to eight channels of digital audio on the outer edges of the 35mm print, outside the sprocket holes. The eight-channel configuration (five screen channels, two surrounds, and an LFE) offered more spatial resolution across the front soundstage than either Dolby Digital or DTS. Last Action Hero was the first SDDS release in June 1993. (wikipedia)

SDDS never achieved significant market penetration. It was consistently the least popular of the three competing digital sound formats — the most expensive to install and the last to arrive. The data's placement on the very edges of the film stock made it vulnerable to physical damage, and only 97 of over 1,400 SDDS-encoded films ever used the full eight-channel capability. Unlike Dolby Digital and DTS, SDDS never developed a home-theater version. Sony ceased manufacturing SDDS hardware in the early 2000s. (wikipedia)

Every digital format kept the analog track as a fallback

All three systems were designed as overlays on existing prints, not replacements. A 35mm print in the mid-1990s might carry Dolby Digital between the sprocket holes, a DTS timecode alongside the analog track, and a standard Dolby SR analog optical track — all on the same piece of film. If the digital reader failed, the projector fell back to analog automatically. This belt-and-suspenders approach reflected the industry's hard-learned lesson from the 1950s: a format that requires universal equipment upgrades before the first print ships will fail.

The 5.1 channel layout became the standard for two decades

Dolby Digital's 5.1 configuration — left, center, right, left surround, right surround, LFE — became the de facto standard channel layout for cinema, and it migrated directly to home formats. DVD adopted Dolby Digital (AC-3) as its mandatory audio codec. DTS offered an optional higher-bitrate alternative on DVD. Both formats used the same 5.1 channel layout that had been designed for theaters.

This standardization meant that for the first time in the history of cinema sound, the channel layout in theaters and the channel layout on home media were identical. The quality differed — theatrical Dolby Digital ran at higher bitrates than DVD, and theater speakers and amplification far exceeded home equipment — but the spatial layout was the same. A 5.1 mix was a 5.1 mix, whether it played in a multiplex or a living room.

Extended surround: 6.1 and 7.1 added rear channels

Gary Rydstrom at Skywalker Sound described the ambition behind pushing digital further:

"'The Phantom Menace' came out after many years of no 'Star Wars' films. My thinking was that if we had a new one, let's push technology and the movie-going experience." — Gary Rydstrom, Variety (2020)

The relationship between Lucasfilm and Dolby was collaborative, not competitive:

"It's a symbiotic relationship with Dolby because we don't compete. They don't make movies, and we don't make sound systems." — Gary Rydstrom, Variety (2020)

Dolby Digital Surround EX, introduced with Star Wars: Episode I — The Phantom Menace (1999), matrix-encoded a rear center channel into the two surround channels, creating a 6.1 layout. DTS-ES offered both a matrix-encoded and a discrete 6.1 option. By the mid-2000s, 7.1 configurations (adding two additional surround channels for a total of four surrounds) became available in larger theaters, and Blu-ray would later support 7.1 channel PCM and lossless codecs.

These extensions were incremental refinements rather than format revolutions. The basic principle — discrete digital channels mapped to specific speaker positions around the room — remained unchanged from Dolby Digital's 1992 debut until Dolby Atmos replaced it with an entirely different paradigm in 2012.