Spatial audio with dynamic head tracking gives users a theater‑like experience for movies and shows, with sound that surrounds them. Using built-in gyroscopes and accelerometers, AirPods Max and your iPhone, iPad, Mac, or Apple TV track the subtle motion of your head, anchoring sounds to your device. Spatial audio creates a three-dimensional (3D) virtual auditory space that allows a user wearing a headset to pinpoint where a sound source is located in the 3D virtual auditory space.

Today the U.S. Patent and Trademark Office officially granted Apple a patent titled "Head-to-Head Rotation Transform Estimation for Head Pose Tracking in Spatial Audio Applications."

Apple's granted patent covers estimating a head to headset rotation transform for head pose tracking in spatial audio applications. In an embodiment, a method comprises: estimating a first gravity direction in a source device reference frame for a source device; estimating a second gravity direction in a headset reference frame for a headset; estimating a rotation transform from the headset frame into a face reference frame using the first and second estimated gravity directions, a rotation transform from a camera reference frame to the source device reference frame, and a rotation transform from the face reference frame to the camera reference frame; estimating a relative position and attitude using source device motion data, headset motion data and the rotation transform from the headset frame to the face reference frame; using the relative position and attitude to estimate a head pose; and using the estimated head pose to render spatial audio for playback on the headset.

Apple's patent FIG. 3 below illustrates the geometry for estimating a head to headset rotation transform auditory space; FIG. 8 illustrates various reference frames and notation for relative pose tracking; and FIG. 9 illustrates the geometry for a relative motion model used in headtracking.

For finer details, review Apple's granted patent 11647352.

Apple Inventors

• Xiaoyuan Tu: Distinguished Technologist
• Alexander Singh Alvarado: Engineering Manager
• Adam Howell: Sr. Motion Engineer