Apple Granted a Patent for an Audio System that Reproduces a Stabilized 'Phantom Center' Audio Channel
Apple's audio team has been busy lately with several patents surfacing. Patently Apple posted a report over the weekend about an advanced multi-speaker audio system designed for TV and live-streaming and another published in April that could be used in an amphitheater, perhaps like the one the Milan Apple Store will have working in the future. In a newly granted patent that surfaced yesterday at the U.S. Patent Office, Apple's latest audio patent covers a system that could one day work with a desktop, a MacBook, a home entertainment system and even an amphitheater. More specifically, Apple's patent covers a system for reproducing a stabilized phantom center audio channel using left and right speaker arrays by separately controlling the directivity of audio signals representing the left and right channels. By doing so the sound would remain centered for the user even if they're not perfectly centered with the display.
Apple notes in their patent background, that in cinema and many home theater systems, sound for front left and front right audio channels is produced by corresponding speakers located respectively to the left and the right sides of a screen or display. Although they may be located outside the screen's boundaries, these front left and right speakers may produce left and right channels with reasonable angular accuracy.
However, a major hurdle for rear-energized or flat video displays is the lack of space for a front center channel speaker coincident with the center of the video display. To accommodate this lack of space, front center speakers have been placed above and/or below the video display. However, since a speaker placed above or below the display is also not coincident with the center of the display, the center channel sound may appear too high or too low.
Apple's newly granted patent 9,729,992 covers their solution to this problem. Apple notes in their patent filing that in one embodiment, an audio receiver receives a left audio channel, a right audio channel, and a center audio channel for a piece of sound program content. A content processor generates separate sets of audio signals for each of these audio channels for driving corresponding transducers in left and right loudspeaker arrays.
In this embodiment, the content processor generates (1) first center audio signals for driving transducers in the left loudspeaker array to generate a first center directivity pattern, (2) second center audio signals for driving transducers in the right loudspeaker array to generate a second center directivity pattern, (3) left audio signals for driving transducers in the left loudspeaker array to generate a left directivity pattern, and (4) right audio signals for driving transducers in the right loudspeaker array to generate a right directivity pattern. In this embodiment, the first and second center directivity patterns collectively represent the center audio channel while the left and right directivity patterns respectively represent the left and right audio channels.
In one embodiment, the left, right, and center audio channels may be equalized or otherwise adjusted to abate auditory distortions. For example, in one embodiment a peak equalizer may be used for equalizing the center audio channel to eliminate a response dip caused by (1) the summation of the first and second center directivity patterns at the ears of the listener, (2) a delay caused by the separation of the left and right ears of the listener, and (3) sound diffraction and reflections about the head of the listener.
By using the system described above, a center audio channel may be accurately represented by using the left and right loudspeaker arrays. In particular, by driving each of the left and right loudspeaker arrays to generate (1) separate center directivity patterns that collectively represent the center audio channel and (2) separate left and right directivity patterns that represent left and right audio channels, respectively, the system described produces a center phantom image for a listener centered on its axis and in addition that center phantom image stays centered with off axis listening through amplitude-time trading that can be made to occur as a function of the polar pattern of the center directivity patterns of the left and right loudspeaker.
Apple notes in FIG. 6 that "as the listener moves to the right towards the loudspeaker array 4B, the sound level from the left center pattern increases while the sound level from the right center pattern decreases." This will balance the sound even if the user isn't positioned exactly to the desktop's center position. Of course this could apply to future MacBooks, a television and beyond.
Whether this will apply to Apple's next-gen modular desktop, MacBook or even smart TV is not known at this time. The timing of any patented invention to market is never guaranteed.
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