Film Guides / Film formats and cinema tech
Dolby Atmos and cinema sound
How cinema sound grew from mono to surround to object-based audio, and what Dolby Atmos and Dolby Cinema actually add to a screening.
Sound is half the cinema experience, and theater sound systems have changed more over the decades than most audiences realize. Dolby Atmos is the latest big step: instead of sending sound to fixed channels, it places sounds in three-dimensional space, including above your head.
From mono to surround
| Era | System | What changed |
|---|---|---|
| Late 1920s | Mono optical sound | One channel printed on the film beside the image |
| 1950s | Multichannel magnetic sound | Widescreen epics on 70mm and some 35mm prints carried four to six channels |
| 1970s | Dolby Stereo | Four channels (left, center, right, surround) encoded in two optical tracks on 35mm |
| Early 1990s | Digital sound (Dolby Digital, DTS, SDDS) | 5.1 digital surround became standard |
| 1999 onward | 6.1 and 7.1 surround | Extra rear channels for more precise surround |
| 2012 | Dolby Atmos | Object-based audio with overhead speakers |
The ".1" in 5.1 and 7.1 means a separate low-frequency effects channel for deep bass, delivered by subwoofers.
Channels versus objects
In a channel-based mix, the mixer decides which speaker group each sound goes to: left, center, right, left surround and so on. The mix is the same whether the room has eight speakers or eighty in each surround zone.
In an object-based mix like Dolby Atmos, a sound such as a helicopter or a raindrop is an object with position data attached. The cinema's processor works out which actual speakers should play it, based on that particular room's layout. A bed of traditional channels, such as ambience and music, sits underneath the objects.
Key facts about Atmos in cinemas:
- It was introduced in 2012, with Pixar's Brave as the first feature released in the format.
- A cinema Atmos mix can contain up to 128 simultaneous audio tracks (bed channels plus objects).
- A cinema Atmos system can drive up to 64 individual speaker feeds.
- Speakers are added overhead in rows along the ceiling, and surround speakers are individually addressed.
What you actually hear
In a good Atmos room, you notice:
- Sounds that move smoothly overhead rather than jumping between side speakers.
- Rain, wind and crowds that surround you in a more natural way.
- Quiet details, like footsteps behind you, placed precisely.
Atmos is not just about loudness. Many mixers use it most effectively in quiet scenes.
Dolby Cinema
Dolby Cinema is a premium auditorium brand that combines Dolby Atmos sound with Dolby Vision laser projection, which offers high brightness and very deep blacks with high dynamic range. Dolby Cinema auditoriums opened from 2014 and also have specified seating and room design. Other premium brands, including IMAX (see IMAX), use their own sound systems.
Other immersive sound formats
Dolby is not the only company working in this space. DTS:X and Auro 11.1 are other immersive formats used in some cinemas, and IMAX has its own approach. Which system a film plays in depends on the version the distributor supplies and what the cinema has installed.
How it is made
Atmos mixes are created on mixing stages built like small cinemas, during the final mix described in sound for film. The same master can produce versions for 7.1 and 5.1 cinemas and for home Atmos systems.
For the best Atmos experience, sit near the center of the room, not too close to the front, so the overhead and surround speakers are balanced around you. See choosing seats and formats.
