Apple has filed for a patent (number 10,524,080) for a “system to move a virtual sound away from a listener using a crosstalk canceler” that hints at enhanced surround sound features in upcoming HomePods and Macs.
In the patent filing, Apple notes that a virtual acoustic system is one that gives the user the illusion that sound is emanating from elsewhere in an indoor or outdoor space than directly from a loudspeaker (e.g., one that is placed in a room, one that is built into a laptop computer, etc. The tech giant says that audio signal processing for virtual acoustics can greatly enhance a movie, a sports even, a videogame or other screen viewing experience, adding to the feeling of “being there.”
Several known audio processing algorithms, executed by digital processors, modify one or more recorded, synthesized, mixed or otherwise produced digital audio signals in such a way as to position a virtual source according to modeling that is based on human perception of sound, including the role of ear acoustics, other reflecting and absorbing surfaces, distance and angle of source, and other factors.
In the case of headphones, specially processed audio signals (binaural rendering) are sent to left and right ears of a listener without the crosstalk that is inevitably received by the ears when listening to stereo loudspeakers. For viewers and listeners that prefer loudspeakers, for example those that may be built into a laptop computer, a crosstalk canceler is employed in some virtual acoustic systems to produce sounds from multiple loudspeakers in such a way that for example a “left” audio signal is predominantly heard only at the left ear of the listener, and a “right” audio signal is predominantly heard only at the right ear of the listener (by virtue of sound wave cancellation in the air surrounding the listener.)
This allows the left and right audio signals to contain spatial cues that enable a virtual sound to be “positioned” at a desired location between the loudspeakers. Apparently, Apple would like to implement this tech in HomePods and Mac speakers.
Here’s the summary of the patent filing: “An audio processing system has one or more processors that process an audio signal on three paths. The first path has a direct gain and a direct virtual source algorithm operating on the audio signal. The second path has a plurality of early reflection gains operating on the audio signal. Operation with the early reflection gains produces a plurality of early reflections.
“Each of the early reflection signals may be subjected to a delay and may be processed according to an early reflections virtual source algorithm. The third path has a reverb gain and binaural reverb filters operating on the audio signal. The third path also has a crosstalk canceler. A mixer combines left and right channel outputs of each of the first path, second path and third path. The mixer produces a left loudspeaker signal and a right loudspeaker signal.”