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AES Germany Section - The Williams Tree, the True 3D Audio Main Microphone Array designed to replace the much-overrated Decca Tree
The ‘Williams Tree’, is based on the process of segmentation of the sound field around us, each segment being covered by the corresponding pair of microphones within an array. A different approach must be adopted for each part of the 3D coverage – the surround sound segments, the side height coverage, and the top zenith zone coverage. This 3D audio array has been developed over a period of about 30 years, and is a carefully constructed array of microphones covering each segment of the sound field, and producing a smooth and accurate natural sound image of the complete spatial image around us. This can be limited to only the upper hemisphere, or it can also cover the lower part of the sound image below the surround sound layer of microphones. The quality of the complete 3D sound image is infinitely superior to the Decca Tree, and promises to become the standard approach to the recording and the reproduction of 3D Audio. However, it must not be forgotten that the recording array is only half the problem, equal attention must be given to the loudspeaker configuration, if optimum results are to be obtained.

The idea for the Decca Tree started in the 1950s in the early days of Stereophonic Recording. Due to Angular Distortion of the reproduced stereo recordings, people came to the conclusion that there seemed to be a hole in the centre of the stereo image. It was therefore quite logical to introduce a third microphone, pan-potted to the centre. In those days, this was seemingly a satisfactory solution to the stereo reproduction problem. But in fact, the Decca Tree was little more than a set of pan-potted omnidirectional microphones. The introduction of the Decca Tree into surround sound recording and later into 3D or immersive sound recording and reproduction, but with no real psychoacoustic analysis of real segment reproduction, was a completely unsatisfactory approach to trying to record and reproduce the spatial aspects of sound.
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