Concentric HRTF Spheres for Multi-Distance Audio Object Placement
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Solution Overview
Problem
Current HRTF calibration systems are limited in their ability to accurately place audio objects at desired perceived distances in space from a listener, as they can only emulate distances up to the outer edges of the sphere defined by the ring of speakers during calibration.
Innovation Solution
A system that uses multiple sets of head-related transfer functions (HRTFs) associated with different radial distances from a location, allowing for the selection and processing of audio objects at specific distances by selecting the appropriate HRTF set or interpolating between sets, enabling more precise placement of audio objects in three-dimensional space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single sphere of speakers is used for HRTF calibration, then the system complexity is low, but the perceived distance range for audio objects is limited to the outer edges of the sphere
Solution Approach 1:
The single sphere of speakers is segmented into multiple concentric spheres, each calibrated at a different radial distance. This allows the system to handle different distance ranges separately, improving perceived distance accuracy for audio objects at various distances while managing complexity through modular calibration procedures
Solution Approach 2:
The system transitions from a two-dimensional sphere surface to a three-dimensional volumetric space by adding multiple radial distance layers. This enables audio objects to be placed not just on the sphere surface but throughout the entire spherical volume, expanding the perceived distance range from the listener
2Adaptability or versatility
If multiple sets of HRTFs at different radial distances are implemented, then audio objects can be placed at desired distances beyond the single sphere limit, but the calibration process and data storage requirements increase
Solution Approach 1:
Multiple concentric spheres share the same spatial coordinates and angular parameters, allowing a single HRTF data structure to serve multiple distance ranges. The system uses universal spherical coordinate systems across all spheres, enabling flexible audio object placement throughout the volumetric space without requiring separate coordinate systems for each distance range
Solution Approach 2:
The HRTF data structure is organized in a nested hierarchy where multiple radial distance sets are contained within a unified spherical coordinate framework. Each concentric sphere's HRTF data is nested within the overall multi-sphere structure, allowing efficient storage and retrieval by distance range while maintaining data organization
Data Source
AI summary
Concentric rings of speakers in a room are activated in sequence to emit test sounds that are picked up by microphones placed in the ears of a listener in the middle of the room. The output of the microphones is used to generate plural HRTF spheres that are concentric, and that can be convolved with each other to render a multi-distance HRTF filter that can be configured to “move” the perceived distance and bearing of audio objects “inside” the outer sphere as desired, without being restricted to placing the audio objects at the outer edges of a single sphere. Any desired placement of an audio object between spheres is done by interpolating between respective coefficients of the closest spheres.