Inertially Stable Virtual Auditory Space for Spatial Audio
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Solution Overview
Problem
Existing spatial audio systems face challenges in maintaining a stable 3D auditory experience when the source device and headset move relative to each other, leading to misalignment of audio sources during head movements, especially in environments like buses or planes.
Innovation Solution
The system uses a method where a spatial audio ambience bed is initialized and tracked using both source device and headset motion data, with the ambience bed rotated about a boresight vector to align with the center channel and kept level with the user's ears, ensuring that the estimated gravity direction remains consistent, thereby maintaining audio channel positions relative to the user.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single IMU in the headset is used for head pose tracking, then the device complexity is reduced, but the audio stability deteriorates during source device motion
Solution Approach 1:
The patent combines data from multiple IMUs (one in the headset and one in the source device) to achieve stable audio tracking. By merging the motion data from both devices, the system compensates for source device motion while maintaining head pose tracking accuracy, resolving the contradiction between system complexity and audio stability.
Solution Approach 2:
The patent introduces an intermediary computational process that uses the motion data from both IMUs to calculate a compensated head pose. This intermediary calculation layer processes the combined data to produce stable audio output, acting as a mediator between the raw sensor data and the final audio rendering.
2Ease of operation
If the source device and headset are allowed to move relative to each other (e.g., on a bus or plane), then the ease of operation is improved, but the audio alignment deteriorates
Solution Approach 1:
The patent implements a dynamic tracking system that continuously adapts to relative motion between the source device and headset. By dynamically adjusting the audio rendering based on real-time motion data from both IMUs, the system maintains precise audio channel alignment even during device mobility, allowing users to move freely while watching content on a bus or plane.
3Measurement precision
If head pose tracking is performed without compensating for source device motion, then the measurement precision is improved, but the virtual auditory space stability deteriorates
Solution Approach 1:
The patent applies a counterweight approach by using the source device IMU data to compensate for and counteract the effects of source device motion on the virtual auditory space. The system calculates the opposite of the source device motion and applies it to the audio rendering, effectively canceling out the destabilizing effects while preserving accurate head pose measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively compensates for the motion of the source device and headset, keeping the audio sources aligned and stable during head movements, preventing virtual audio sources from appearing higher on one side when tilting the head.
Implementation Method 1
determining a gravity direction using acceleration measurements output by an accelerometer of the source device
Implementation Method 2
predicting an attitude of the source device based on a rotation rate of the source device and the reference gravity direction, wherein the rotation rate is output by an angular rate sensor of the source device
Data Source
AI summary
During an initialization of a head pose tracker for a spatial audio system, a spatial audio ambience bed is rotated about a boresight vector to align the boresight vector with a center channel of the ambience bed. The boresight is computed using source device motion data and headset motion data. The ambience bed includes the center channel and one or more other channels. An ambience bed reference frame is aligned with a horizontal plane of a headset reference frame, such that the ambience bed is horizontally level with a user's ears. A first estimated gravity direction is fixed (made constant) in the ambience bed reference frame. During head pose tracking, the ambience bed reference frame is rolled about the boresight vector to align a second estimated gravity direction in the headset reference frame with the first estimated gravity direction fixed in the ambience bed reference frame.