A Brief History of Film Sound Since the introduction of sound with film in 1927, there has been a steady evolution of technology used to capture the artistic intent of the motion picture soundtrack and to replay it in a cinema environment. In the 1930s, sync sound on disc gave way to variable area sound on film, which was further improved in the 1940s with theatrical acoustic considerations and improved loudspeaker design, along with the introduction of multitrack recording and steerable replay (using control tones to move sounds). In the 1950s and 1960s, magnetic striping of film allowed multichannel playback in theatres, introducing surround channels and up to five screen channels in premium venues. In the 1970s, Dolby introduced noise reduction, both in postproduction and on film, along with a cost-effective means of encoding and distributing mixes with three screen channels and a mono Surround channel, as shown in the following figure. The quality of cinema sound was further improved in the 1980s with Dolby SR noise reduction and certification programs such as THX®.
The 1990s saw the launch of digital sound to the cinema, allowing 5.1 mixing, mastering, and playback providing discrete Left, Center, and Right screen channels, Left Surround and Right Surround arrays, and a Low-Frequency Effects channel played through a subwoofer.
In 2010, the first step in enhancing digital cinema sound was undertaken with the introduction of Dolby Surround 7.1. This format continues the pattern of increasing the number of surround channels by splitting the existing Left Surround and Right Surround channels into four “zones,” as shown in the following figure.
How Dolby Atmos Works Its Magic
Picture above with various colors indicating speakers that are strategically placed throughout the theater. Solid Red indicates existing Surround Speakers, Red with speaker insignia indicates existing Screen Loudspeaker, rectangular Blue indicates additional Top Surround, square Blue is additional Side Surround, Purple with speaker insignia is Surround Subwoofer and lastly in Green indicates optional Screen Loudspeaker.
A More Effective Speaker Setup
The most immediately noticeable difference in a Dolby Atmos system is the use of overhead speakers, but that's just part of the story.
A typical surround sound system consists of left, center, and right discrete channels with the speakers behind the screen. The surround channels are handled by wall-mounted arrays of speakers, divided acoustically into two or four zones. All speakers within a zone receive the same audio information.
In a Dolby Atmos theatre, every speaker—as many as 64 total—is powered independently and gets its own separate audio feed. In effect, each speaker is its own zone. In addition to the overhead speakers, Dolby Atmos typically adds more surround speakers and screen speakers.
Three critical elements significantly improve the audience experience over 5.1 and 7.1 systems:
• Sounds originating overhead
• Improved audio quality and timbre matching.
• Greater spatial control and resolution improvements of Dolby Atmos.
Sounds Gain Their Independence
Making the Bed
Putting It Together
Even More Audio Improvements
The audience can now enjoy a completely new listening experience with enveloping sound that brings the stories on screen more fully to life.