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Implementation of a Proposed 9-Channel (8.1) Sound format for 70mm, 35mm and D-Cinema

The 70mm Newsletter
Written by: Ramon Lamarca Marques, Brian Guckian and Mike Taylor Date: 16.01.2008
This article posits a concept for the practical application of a new 9-channel (8.1) sound format across 70mm and other theatrical exhibition platforms. It builds on and enhances existing techniques used to deliver multi-channel sound in the cinema, in a cost-effective and realistic manner, and with a greater degree of differentiation to home entertainment formats.
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The conventional 5.1 sound format used both for theatrical and home cinema works very well in terms of providing stereo stage channels with a discrete centre, coupled with stereo surrounds and a separate sub-woofer. This format has been very effective in dramatically improving the audio experience in the cinema and home viewing environments, and in recent years has been refined with the addition of a back (or rear) surround channel.

However, 5.1 is of course not the only multi-channel sound format that has been developed for theatrical use, and in large theatres, the advantages of 5 stage channels, with additional Left Extra and Right Extra information, and a Centre that can be kept free from music and effects, have been known since its advent with Cinerama in 1952. The "5 across" configuration gives a far better spatial audio experience in large theatres, as the additional Left Extra and Right Extra channels fill the aural "holes" between the Left and Centre and Right and Centre screen channels for very wide screens. The "5 across" configuration has also been used on several 35mm SDDS releases over the years, and many theatres are equipped for this configuration.

What this article does is to propose, for large screens, a marriage of the traditional "5 across" format with the current enhanced 5.1 format with rear surround, to yield Left, Left Extra, Centre, Right Extra, Right, Left Surround, Right Surround, Back Surround and Sub-woofer channels. This gives a total of 8.1, or in short, 9 channels, with several advantages that will be outlined.

Practical Application

Click image to see enlargement

Adoption of any new sound format in the cinema is dependent on ease of application and ubiquity. It is important that any format be applicable across a range of theatrical release formats to be viable. For instance, it is highly unlikely that mixing time could be allocated affordably to make a 9-channel mix purely for 70mm purposes.

Happily, a 9-channel format can theoretically be accommodated for 70mm digital, 35mm digital and D-Cinema sound formats, which is ideal in today's sound post-production and re-recording environment. Indeed there is very little difference between mixing for 9 channels instead of 8 (as has been done up to now on selected releases); the only addition being the Back Surround channel, which in any case is often provided for when doing mixes for 35mm and home cinema.


Many theatres are already equipped for both "5 across" and Back Surround playback, the only point to note being that both have not been formally used together up to now. Adaptation in these cases to play back formal 9-channel material does not require new speaker runs, speaker assemblies or amplifiers; rather modifications would be made only at the processor end of the system.

This would require manufacturers whose products are theoretically capable of playing back up to 10 channels of audio to offer a hardware upgrade via new cards, outboard units, etc. It is not within the scope of this article to detail exactly how this could be done, but merely to point out that it should be possible and is worthy of consideration. 70mm audio and certain 35mm audio formats are theoretically upgradeable to 10-channel reproduction, whilst D-Cinema accepts up to 16 channels via the DCI specification.

Mixing and Playback Processes

The proposed 9-channel layout is shown in the diagram. Since a 9-channel mix must also be reproduceable in a 5.1 theatre, processors would have to include a "fold-down" function so that the Left Extra, Right Extra and Back Surround channels could be mixed into the 5.1 "envelope" on playback.

This is already done in 5.1 theatres equipped to play back 8-channel mixes in the 5.1 format; in this case the Left Extra and Right Extra channels are apportioned to the Left and Centre and Right and Centre channels, respectively. The Back Surround channel is then simply not reproduced, or if this is problematic then a method of apportioning the Back Surround information between the Left surround and Right Surround channels would have to be found, possibly via another "fold-down" function in the processor.

Cinemas with 5.1 reproduction only may find it economically beneficial to convert one or two large screens to the 9-channel format if this is done at the same time as, for example, a D-Cinema installation. Two-screen capability is advantageous so that films can be transferred after their opening run.

A final consideration is archivability of 9-channel mixes. Happily, it is possible to record up to 10 tracks of audio to 35mm fullcoat mag using the specialised "8+2" head and track configuration. This uses 8 sound records across the the mag between the perforations, with the two additional tracks outside the perforations, on each side of the mag film.

Advantages of a 9-Channel Sound Format

Adoption of 9 channels as a new choice for mixing and theatrical reproduction gives the following advantages:

- Superior spatial reproduction across the large screens increasingly used in multiplex and other cinemas;

- Excellent dialogue clarity as the Centre channel can be kept free of Music and Effects;

- All the advantages of three Surround channels as found on selected 35mm releases;

- Enhanced enjoyment for audiences, with greater artistic possibilities and quality;

- Applicable across 70mm, 35mm and D-Cinema formats, making economic sense;

- Relatively easy to implement whilst not precluding addition of more channels in the future;

- Theatrical format only, providing greater differentiation to the increasingly sophisticated home cinema offering and thus encouraging audiences to choose the theatrical cinema option;

- Facilitates increased use of the 70mm format for limited "roadshow" style engagements of "tentpole" releases.


The advantages and practicality of a 9-channel sound format for 70mm, 35mm and D-Cinema theatrical release platforms have been outlined. Feedback on this article is welcomed; please contact the Workshop Editors.
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Updated 21-01-24