The intent of commercial cinema designers is to fully immerse the audience in a sound field, which entails providing height information as well as the traditional horizontal surround information.

To achieve this, many more speakers than what is currently the norm are needed. In fact, true ‘3D’ sound requires two rows of ceiling loudspeakers running from the screen to back wall. The existing surround arrays are extended forward right up to the screen. And, the surrounds are required to be ‘full range’ so they can be used with bass management.

The key issues for the commercial cinema industry are how to squeeze as many channels as possible into the 14 channels available in the Digital Cinema Package (DCP) Standard and backwards compatibility with existing 5.1, 7.1 and stereo systems.

3D sound systems are a major change for the traditional cinema B Chain. (The term ‘B Chain’ harks back to the dawn of the industry, where the projector, film and optical sound heads were the A Chain and the remainder of the audio was called the B Chain.)

And there are several competing systems emerging – Dolby Atmos, the Barco Auro 3D and the Fraunhofer Institute IOSONO, along with the venerable NHK 22.2.

The goal of these systems is to not only surround the listener with audio but to introduce point source audio within the audience space. Put simply, imagine a cat fight going on in a movie. We currently hear the cat fight emanating from the speakers around the audience but with 3D sound the cat fight can sound like it is happening in a specific place inside the theatre.

Immersive sound has been researched for many years by the Japanese broadcasting organisation NHK as an adjunct to its Super Hi-Vision next generation television system project. Its research indicated that loudspeakers in the horizontal plane needed to subtend angles of 45º or less to create seamless transfer of sound images. A similar angle is needed in the vertical plane and they found a configuration of three layers of surrounds – top, middle and bottom – was needed, comprising 22 loudspeakers.

The 0.2 in the name is for two channels of subwoofers/LFE.

To date, NHK has developed a suite of tools and techniques for capturing the sound and processing it in 3D, to create the effects desired by sound mixers. But, since the 22.2 system is based in television, there are some practical difficulties in persuading home owners to install this large number of loudspeakers, so they have developed a conversion/downmix to eight channels.

The Fraunhofer IOSONO was developed from research into wave field synthesis, a technique using a lot of loudspeakers (up to 256) around the walls of a room and extensive Digital Signal Processing (DSP) in order to create sound sources at any point inside the room. For 3D sound in cinemas, it has evolved to use about 50 speakers around the walls and additional ceiling speakers for height information. Sound is stored and mixed as an array of objects so it is possible to translate or render the final effect for rooms of different sizes. This has necessitated the development of suitable software tools for the creation of the content.

Dolby has taken advantage of the new Digital Cinema Package (DCP) to fully use 14 digital channels to create 3D sound. It was mindful of backwards compatibility, so it extended the existing left and right side surrounds up to the screen and added a double row of ceiling surrounds from screen to rear wall. To minimise the change of timbre often noticed between the screen systems and surrounds, Dolby specifies that the surrounds must be able to reproduce the full frequency range. This can involve a bass management system and rear subwoofers (LFE).

For content creation, Dolby has developed a new way of describing audio content, that of audio objects, which separates the artistic intent of positioning the sound in space form the way it is rendered in the room. The audio is a combination of ‘essence’ (content) and metadata. The file structure allows for audio as a set of traditional channels, now called ‘beds’, or a sequence of audio objects, or some combination of the two. The file describes where the audio objects should be placed, their apparent size and their movement.

The system channel-based ‘beds’ are in essence screen or surround sub-mixes intended for traditional loudspeaker positions.

Individual objects, targeted at more controllable locations, can be overlaid on these ‘beds’ for more precise spatial control over specific sound effects. The system can have up to 128 tracks in the studio environment, and the composite file structure on play back can be rendered into a maximum of 64 channels depending on the size of the cinema.

The Barco Auro-3D system started as a height extension technique and it has found that having five loudspeakers in a bottom layer plus four in an upper layer gives an impressive and well balanced solution – the original Auro 9.1 format for home cinema setups.

This has evolved through 11.1 to 13.1 for commercial cinema. It has the advantage of compatibility with the existing standards, which means no change in the distribution format or hardware. The Auro format essentially uses a channel based approach, which has advantages in terms of simplicity, direct control over the final master and ease of implementation in the cinema. The additional channels are delivered in the 5.1 channel PCM data stream, encoded in a proprietary fashion into the least significant bits of the bit stream using a purely mathematical process.

All of these competing formats remind me of the HD DVD versus Blu-ray and Beta versus VHS format wars. With so many formats competing for cinema business, a clear leader will eventually emerge. The biggest issue is the studio work flow in the creation of content. At home you would not like to have to own four different players just to watch your movies depending what format they were in. For a cinema owner, the same thought process applies. Multiply this issue by thinking of all the big movie houses that make these films having to record and master in all the different formats. The winner in this battle will be the format that gets the most movie houses on side and producing in its format, much the same as Blu-ray did for the consumer market.

The result of all this development and background engineering will be an amazing audio experience at a 3D cinema in the near future.