Lucasfilm is using the soon-to-be-opened San Francisco Bay Bridge as a sound recording studio, obtaining underground audio that could be utliized in a myriad of ways and productions in the future.
Explains PSFK, "Crawling into one of the concrete pillars sunk beneath the San Francisco Bay, the Skywalker Sound team is firing blanks from a pistol inside the cavernous structure to record a sonic impulse response, or an audio impression...[Skywalker] is using the recordings to build their audio database for future films and other projects. Through the use of their state of the art equipment, and the acoustics of the bridge, Skywalker is able to record a full range of audible frequencies. Back at the studio, they can then digitally remove the sound of the gunshot, leaving them with a complete acoustical audio impression."
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