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技术介绍 |
Wave field synthesis (WFS) is a spatial audio rendering technique, characterized by creation of virtual acoustic environments. It produces "artificial" wave fronts synthesized by a large number of individually driven speakers. Such wave fronts seem to originate from a virtual starting point, the virtual source or notional source. Contrary to traditional spatialization techniques such as stereo or surround sound, the localization of virtual sources in WFS does not depend on or change with the listener’s position. The Moving Picture Expert Group standardized the object-oriented transmission standard MPEG-4 which allows a separate transmission of content (dry recorded audio signal) and form (the impulse response or the acoustic model). Each virtual acoustic source needs its own (mono) audio channel. The spatial sound field in the recording room consists of the direct wave of the acoustic source and a spatially distributed pattern of mirror acoustic sources caused by the reflections by the recording room surfaces. Reducing that spatial mirror source distribution onto a few transmitting channels causes a significant loss of spatial information. Much more accurately this spatial distribution can be synthesized by the rendition side. Concerning the conventional channel-orientated rendition procedures, WFS provides a clear advantage: "Virtual panning spots" called virtual acoustic sources guided by the signal content of the associated channels can be positioned far beyond the material rendition area. That reduces the influence of the listener position because the relative changes in angles and levels are clearly smaller as with closely fixed material loudspeaker boxes. This extends the sweet spot considerably; it can now nearly cover the entire rendition area. The procedure of the wave field synthesis thus is not only compatible, it clearly improves the reproduction for the conventional transmission methods. Loudspeaker arrays implementing WFS have been installed in some cinemas and theatres and in public range with good success. The first live WFS transmission took place in July 2008, recreating an organ recital at Cologne cathedral in lecture hall 104 of the Technical University of BerlinThe room contains the world’s largest speaker system with 2700 loudspeakers on 832 independent channels. Development of home-audio application of WFS has only recently begun.In spite of the efforts, large acceptance problems remain. |
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