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NHK pushes surround to 22.2 channels

NHK has devoted great resources to technology development to push audio and video systems beyond known limits. As part of its recent efforts to erase the boundaries of both audio and video resolution, the company has devised a 22.2 multichannel sound system.

This system was intended to serve as a truly immersive audio experience in support of its ultra-high-definition video technology, often referred to as Super Hi-Vision (SHV).The challenge in creating a 22.2 multichannel system laid as much in the playback and manipulation of the signals as it did in determining how many channels were needed and where to put them.

First, a quick review of what SHV is. The spec calls for 4000 scanning lines, which, among other things, has the effect of broadening the viewing angle to a 100-degree horizontal beyond what standard high-definition offers. It has 16X the resolution of HDTV and more than twice the resolution of 70mm motion picture film. Demonstrations in Japan have featured program content viewed on a 600in screen.

So, a top-to-bottom surround system was needed that exceeded what was possible with conventional 5.1 and 7.1 surround systems. After a great deal of theorizing and experimentation, one solution was the 22.2 multichannel system. The system has three layers of loudspeakers, which creates a more natural three-dimensional sound field enhancing presence and the sense of reality.

The three layers include:

  • an upper layer of nine channels arrayed on the front, back and sides
  • a middle layer of 10 channels arrayed in similar fashion
  • a lower level of three channels, situated under the screen in front, which is where the two LFE channels are as well.

It is probably obvious that producing program material for something so complex on standard equipment and using standard surround techniques would not work. Even with standard surround sound, production techniques would be too time-consuming because of the repetition of several processes. And even then, the method would still fail to create the desired sound fields for reflecting natural situations.

What it boils down to is that the engineers determined that all sound effects, except for lateralization, are realized through a combination of direction control and distance control of sound images. Furthermore, the mixing and monitoring busses on standard tools do not provide exclusive channels for lateralization effects. Thus, multichannel sound production would be easier if the tools being used could effectively control distance and direction to a sound source.

The perceived distance to a sound source is determined by three factors: loudness, tone color and reverberation. The control surface of a mixing console that could accommodate these parameters would need to have two controls on each channel strip. These double faders would not function as an in-line console.

Instead, the lower fader function works the same as a conventional fader to control the level of the input signal, and the upper fader exclusively controls the distance of the sound image. If the sound engineer wishes to put the sound image far away, he or she simply puts the fader up to the desired position where it creates the desired sense of distance. The distance fader controls these three functions for each channel.

Fairlight's Constellation XT console with its In-Line Panel (ILP) option offers advanced software flexibility and was easily modified to handle the task. The ILP is, in effect, comprised of 72 soft knobs and displays. It is therefore relatively simple to customize software for all the busses required to accomplish the need for multiple faders per channel.

The console can be viewed with 24 additional busses or auxes for the 22.2 feeds. Because of the software, it's also relatively easy to modify the buss structure in the console to do any combination of busses desired for such multilayered effects. This is possible because there is a macro language in the system that enables engineers to change key functions and create bussing structures that are different than a stock system.

Fairlight's soft approach to knobs and displays is serving as NHK's model for manipulating both standard fader functions and programmable channel functions, such as the distance, depth, vertical and lateralization effects needed in the 22.2 multichannel system. The end result is an impressive visual and sound experience that pushes audio and video past previous limits.

Tim Wetmore is a New York City-based freelance writer covering the entertainment and communications technology industries.