Dolby Atmos: The Future of Cinemas

Photo by Ernesto Andrade CC BY

Sound effects have become an integral part of modern films. Every year they are becoming more realistic, and what we hear now in the cinema is the result of the hard work of many people over the course of a century.
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However, with the proliferation of the Internet and the emergence of services such as Netflix, the popularity of cinemas began to decline gradually. In an attempt to support this type of business, several new technologies were implemented. Along with IMAX, which offers a high-quality 3D image, interesting solutions also appeared in the field of sound.

According to experts, the new milestone in the development of cinema will be the format of multi-channel sound Dolby Atmos. Presented Dolby Atmos in the famous Hollywood movie theater Dolby Theater in April 2012. The first picture, whose soundtrack was made in this format, was the cartoon "Brave Heart" ("Brave") studio Pixar. Although in 2012 the number of cinemas using Atmos did not exceed 25 pieces worldwide, in 2013 their number increased to 300 and continued to grow.

Since “Braveheart”, films such as “Guardians of the Galaxy”, “Star Trek: Retribution” and “Life of Pi” have been made using the new technology. Brett Crockett, director of the Dolby sound research laboratory, said: “Dolby Atmos is the first audio system for the cinema that is not based on channels, but on audio objects.” Atmos is different from other existing multichannel standards in an interview with the American magazine Sound & Vision. The crying child, the sound of a helicopter, the horn of a car — these are all audio objects. ”

Sound engineer, using Dolby Atmos, decides where exactly the sound source is (in other words, make up a 3D map of the sound space), and determines which path it takes. It turns out that you can choose from which speaker the sound will come. If the required speaker is inoperative or absent, the system will automatically generate a “phantom” loudspeaker so that the sound will still come from the right place.

Thus, the content in the cinema is not in the form of pre-recorded tracks, but in the form of a large number of sound files and the corresponding information about the space-time coordinates. This information enters the sound processor, which knows exactly where the acoustic systems are located (installed and calibrated during the installation of the cinema hall), and calculates itself where and what sound information should be sent.

The tiny white line on top of the cube represents a flying helicopter in 3D space. The points on the left represent the dynamics. The subwoofer and the two left upper speakers are active at this moment.

In addition to audio objects, Dolby allows you to work with conventional sound channels (Beds) that do not require spatial coding (environmental noise, music), which allows you to create the most complete immersive picture.

For each cinema, a project is created in accordance with the specifications, where the number and location of the speakers needed to correctly reproduce the format is determined. Each such project is approved by an authorized Dolby consultant.

In general, Dolby keeps all projects under direct control. Cinema halls are approved by Dolby experts, who go to the site, measure and accept the hall. When this happens, it checks the configuration and equipment - each speaker and amplifier.

The company representatives have a special measuring system consisting of 8 microphones, which records the parameters and the delay of the sound of each loudspeaker. If all the acoustics is approved, then the process of grouping into 5.1, 7.1 and 9.1 arrays begins. After that, the configuration of the hall is stored in the processor, the configuration protocol is filled. In other words, in order to give the hall the status of Dolby Atmos, the company checks all the characteristics.

When configuring the processor, data about the size of the hall, the number and coordinates of the placement of the speakers, all characteristics of the speakers and associated amplifiers, etc. are entered. The room is described for the processor so as to eliminate the possibility of errors ( video ).

Dolby Atmos allows you to work with 128 audio tracks, which are processed depending on their type. Static tracks are immediately “assigned” to individual speakers or their whole arrays. As for the audio objects, they are processed in real time according to the configuration of the cinema hall. Total Dolby processor allows you to output sound to 64 speakers simultaneously.

Audio equipment and halls in various cinemas can differ dramatically in size and shape, so that the sound is maximum pleasure, the developers have prepared the requirements for the placement of acoustic systems.

To make sound transitions as smooth as possible, the company recommends installing two additional speakers behind the screen (marked green in the layout of the sound equipment) - this is especially important for cinema halls whose screen width exceeds 12 meters. Also, all the "screen" horns should be deployed at one particular point, located somewhere in the hall, to cover all seats.

Frontal subwoofers are grouped into a single array of desired power, which is slightly shifted away from the axis of symmetry - this reduces the likelihood of standing waves.

As for the ambient speakers located along the walls, they must be connected to an individual amplification channel, adjusted in accordance with the parameters of the maximum noise power specified by the manufacturer of audio equipment.

Side audio systems should be located along the entire length of the wall to provide decent sound coverage, and form a straight line, as shown in the figure below. The inclination of the speakers should be oriented along the axis to the ear of the spectator, sitting at the extreme place at the opposite side of the hall.

Most surround speakers are not capable of producing powerful low frequencies, so two additional subwoofers should be added to the back of the audience.

As for the ceiling acoustics, the upper speakers should be located strictly symmetrical with respect to the axis of the hall and along its entire length. Moreover, the distance between the two rows of speakers should be slightly larger than between additional speakers behind the screen. Again, the speakers in the front and back of the audience should be turned towards a common point.

According to Dolby, a spectator sitting in a well-equipped hall has the feeling that he is “surrounded by an infinite number of speakers” - this allows him to immerse himself in what is happening on the screen.

Rui Soares and Dipankar Grover say that the technology gives a great impression and distinguishes the Atmos system from other systems easier than the easy one. “Dolby Atmos can take you right into the thick of the events happening on the screen,” Grover exclaims.

However, the system can give such magical impressions only if the equipment is properly adjusted and the correct sound levels are set. Otherwise, the technology turns into another way of “processing” the viewer with a loud sound, simply from an even greater number of directions.

The sound is an interesting thing. It is incredibly important for the perception of the film, however, when done correctly, you do not even notice it. However, if you still pay attention to him, then you will discover many interesting things. Sound is the main weapon of cinemas, which requires as much attention as a movie picture, and Dolby Atmos technology has great potential in this area.

PS More materials on the topic of audio - in our blog " Hi-Fi World ".