Apple has been granted a patent (number 10,609,485) for a “system and method for performing panning for an arbitrary loudspeaker set-up” that’s designed to make it easier to pair HomePods, as well as create an addition “virtual loudspeaker.”
The patent involves “ambisonics,” is a surround sound technique based on spherical Fourier expansion of the sound field. Ambisonics is used to represent a 3D sound field for scene-based audio. This representation can be performed using first order Ambisonics (FOA) or higher order Ambisonics (HOA.) A sound source can either be encoded in an ambisonic format, or it may be recorded via a special microphone. Such a representation of the sound field may then be transmitted to an end user machine where it is decoded for playback.
Conventional ambisonic decoders require an optimally placed fixed loudspeaker setup which, per Apple, means that the decoders can’t perform well with arbitrary loudspeaker setups.
The patent also involves “panning,” the distribution of a sound signal into a new stereo or multi-channel sound field, as determined by a pan control setting. Apple says that existing panning techniques have some limitations. For example, the existing panning techniques don’t perform well when loudspeakers are not distributed in a way that fully encompasses the listening position (e.g., horizontal loudspeaker setups, frontal only setups, etc.).
Apple says that eExisting panning techniques only perform well when the panning trajectory is within the span of the loudspeakers. Some loudspeaker setups impose limitations on more complex panning trajectories, such as when trying to pan a sound source in 3-dimensional space while the loudspeaker setup spans only a 2-dimensional space.
Apple wants a set of HomePods to communicate to overcome such limitations. It also wants its Macs, iPhones, iPads, and Apple TVs working with the speakers to be able to a virtual loudspeaker or virtual acoustic system that works by using crosstalk canceling. This would make users feel like sound is coming from a different place than loudspeakers.
Here’s the summary of the invention: “Placement of one or two placed virtual loudspeakers within a loudspeaker setup that includes a real loudspeakers is determined and vector base amplitude panning (VBAP) gains including the gains of the real loudspeakers and placed one or two virtual loudspeakers are also then determined. Gains of one or two placed virtual loudspeakers are redistributed to the real loudspeakers to ensure preservation of total energy.
“Real loudspeakers in the loudspeaker setup have redistributed gains of one or two placed virtual loudspeakers. Loudspeaker outputs are generated and transmitted to the real loudspeakers to be played back. When received audio content is ambisonics content, a predetermined grid is generated and HOA content is projected to the grid.”