Cinema's Hidden Multi-Channel History and the Origins of Digital Surround

It was at the 1987 October SMPTE meeting. People were saying, “How many channels should there be [in the digital sound standard for cinema]?” And people said two . . . people said four . . . one said eight. And I put my hand up and said, “five point one.” Everybody went, “What is he talking about?”
– Tomlinson Holman, audio engineer and inventor of THX

Cinema’s Hidden Multi-Channel History and the Origins of Digital Surround

The Origins of Multi-channel

Advances in technology
Aesthetic experimentation
Economics of exhibition
Audience expectations
Growth of home systems

Milestones in Multi-Channel Cinema Sound

1881: Clément Ader’s Théâtrophone – 2-channel opera relays in Paris.
1931–35: Bell Labs (Harvey Fletcher/Stokowski) + Blumlein stereo experiments.
1937: Universal’s One Hundred Men and a Girl recorded multi-channel (released mono).
1940: Fantasia – Fantasound (3 screen + surround, ~64 speakers).
1952: Cinerama – 7 channels (5 screen, 2 surround).
1953: CinemaScope – 4-track mag (L, C, R, surround).

1955: Todd-AO 70 mm – 6-track mag (Oklahoma!).
1974: Sensurround (Earthquake).
1975: Dolby Stereo (LCRS matrixed to Lt/Rt).
1977–79: 70 mm six-track “baby boom” (Close Encounters, Superman, Apocalypse Now).
1982/87: Dolby Surround & Pro Logic (home).
1990: Cinema Digital Sound (CDS).
1992–93: Dolby Digital, DTS, SDDS arrive.
1994: ITU codifies 5.1 (3/2 with LFE).
1995: LaserDisc AC-3 = first consumer discrete 5.1.
1997: DVD mainstreams 5.1.

Widescreen & Magnetic Sound (1950s)

What is Matrixing?

A method to fit more channels into fewer tracks.
Example: Dolby Stereo (L, C, R, S) encoded into two optical tracks (Lt/Rt).
Uses phase and amplitude relationships so a decoder can “steer” sounds back into their intended channels.
Ensures backward compatibility: a mono or stereo theater can still play the same print.

Concept: Matrixing is a clever workaround for physical limitations of film. A 35 mm optical soundtrack could only hold two tracks, but Dolby wanted four (L, C, R, S). By manipulating amplitude and phase, they folded four channels into two “Lt” and “Rt.” A decoder (Dolby Pro Logic in theaters, later at home) could then re-expand them into approximate four-channel playback.

How it works:

Center: equal signal in Lt and Rt, in phase.
Surround: equal signal in Lt and Rt, but phase-shifted ±90°.
Left and Right: carried primarily in Lt or Rt, as in stereo.
Decoder detects phase/amplitude cues and steers to correct speaker.

Limitations:

Crosstalk: sounds could bleed into the wrong channel.
Band-limited surrounds: ~100 Hz–7 kHz to reduce audible artifacts.
Steering artifacts: strong signals could pull ambiguous sounds into center or surrounds unexpectedly.

Advantages:

Cheap: no need for magnetic prints.
Compatible: worked in mono or stereo theaters without upgrade.
Transitional: gave audiences a taste of surround until discrete digital arrived.

Discussion prompt for students:
Why was backward compatibility (prints playable in any projector) more important than perfect sound quality in the 1970s? How do we see similar compromises in today’s media formats (e.g., streaming codecs, HDR video)?

Dolby Standardizes Surround

Dolby Stereo Logo

Four channels (L, C, R, mono surround) matrix-encoded into 2 optical tracks.
Debut: Lisztomania (1975).
Widely popularized by Star Wars (1977), Close Encounters (1977).
Surround limited to 100 Hz–7 kHz.

The Limits of Dolby Stereo

Earthquake (1974) & Sensurround

Digital Surround’s Pre-History

1987 SMPTE: call for discrete, CD-quality audio.
Tom Holman proposes “5.1” channel layout.
1992/94 ITU codifies 5.1 (3/2 with LFE).

Cinema Digital Sound (CDS, 1990)

Digital Sound Arrives in Triplicate

Dolby Digital (SR-D, 1992): Data between sprockets + analog fallback. First: Batman Returns.
DTS (1993): Audio on CD-ROM synced by timecode. First: Jurassic Park.
SDDS (1993): Sony’s 7 channels (5 screen + 2 surrounds). Data on film edges.

Surround Sound Moves to the Home

1982: Dolby Surround (Lt/Rt home decoding).
1987: Pro Logic (adds center, steering).
1995: LaserDisc AC-3 introduces discrete 5.1.
1997: DVD mainstreams 5.1.
2000s: explosive home theater growth.

Variations in 5.1 Configurations

Epilogue: From 5.1 to Objects

Atmos, DTS:X, MPEG-H extend 5.1 with height and objects.
ITU 5.1 remains the global reference layout.
Future questions:
- Will object-based replace channel-based?
- How do we mix for theaters, homes, headphones simultaneously?

Extra Discussion Questions (if time permits)

Standards vs. Innovation

Why did 5.1 become the global standard instead of other proposed layouts?
What are the trade-offs between adopting a “good enough” standard and pushing for technically superior alternatives?

Matrixing vs. Discrete

Dolby Stereo relied on matrix encoding while later systems went fully discrete.
Can you think of other media technologies where compression or “tricks” were used until a discrete alternative became affordable?

Spectacle vs. Fidelity

Fantasia and Sensurround show different priorities: realism versus impact.
Which approach dominates today’s cinema sound design? Do you think audiences value accuracy or “wow factor” more?

Home vs. Theatrical Listening

How do differences between cinema arrays and home point-source speakers shape the way films are mixed?
What compromises might sound designers make knowing their mix will be heard in both contexts?

Future Formats

Atmos and DTS:X expand beyond 5.1 to object-based systems.
Do you think object-based sound will fully replace channel-based standards, or will 5.1/7.1 remain the backbone?