Adaptive Eigenbeamforming Microphone Array for 3D Sound Field Control
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Solution Overview
Problem
Conventional microphone arrays face limitations in 3D space steering, computational complexity, and beampattern control, particularly in spherical eigenbeamforming, where spatial aliasing and finite harmonic extraction restrict the accuracy and flexibility of sound field decomposition and reproduction.
Innovation Solution
A spherical microphone array with a truncated icosahedron geometry and adaptive audio system that employs spherical harmonic decomposition, allowing for continuous 3D beampattern steering using modal decomposer and beamformer stages, reducing computational cost by using one filter per spherical harmonic and enabling accurate control over beampatterns through discrete orthonormality and frequency compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If spherical harmonic decomposition is used for sound field decomposition, then 3D space steering capability is improved, but spatial aliasing and finite harmonic extraction limit the accuracy
Solution Approach 1:
The patent applies frequency compensation by changing the frequency response parameters of the eigenbeams to compensate for the limitations of finite harmonic extraction. This involves applying frequency-dependent weightings to the spherical harmonic components to restore accuracy across different frequencies, thereby resolving the contradiction between 3D steering capability and decomposition accuracy.
2Device complexity
If conventional beamforming is used, then computational complexity is high, but spherical eigenbeamforming reduces computational cost
Solution Approach 1:
The patent segments the beamforming process into two distinct stages: modal decomposition (spherical harmonic transformation) and modal beamforming (eigenbeam combination). This segmentation allows the computationally intensive decomposition to be performed once, with subsequent beamforming operations being more efficient, thus reducing overall computational complexity while maintaining reliability through the structured two-stage approach.
3Adaptability or versatility
If spherical microphone arrays are used, then arbitrary beampattern control is enabled, but spatial aliasing restricts the flexibility
Solution Approach 1:
The patent introduces frequency compensation as an intermediary processing step between spherical harmonic decomposition and beamforming. This intermediary stage applies frequency-dependent corrections that mitigate spatial aliasing effects, allowing the system to maintain flexible beampattern control while reducing the harmful effects of spatial aliasing that would otherwise restrict this flexibility.
Data Source
AI summary
An exemplary audio signal processing system includes a modal decomposer and an adaptive modal beamformer. The modal decomposer generates a plurality of zeroth-order eigenbeams from audio signals from an (e.g., spherical) array of audio sensors. The adaptive modal beamformer (i) steers the zeroth-order eigenbeams to a specified direction, (ii) adaptively generates a plurality of weighting coefficients for the plurality of zeroth-order eigenbeams, where the plurality of weighting coefficients satisfy a constraint of having only non-negative values, (iii) respectively applies the plurality of adaptively generated weighting coefficients to the plurality of steered, zeroth-order eigenbeams to generate a plurality of weighted, steered, zeroth-order eigenbeams, and (iv) combines the plurality of weighted, steered, zeroth-order eigenbeams to generate an output audio signal. Some embodiments have a further constraint that the weighting coefficients sum to a specified value (e.g., one).