Adaptive Filtering for Spatial Sound Reproduction
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Solution Overview
Problem
Spatial sound field reproduction techniques, such as wave field synthesis and Ambisonics, face limitations in achieving high-quality spatial sound reproduction due to the need for a large number of loudspeakers and the imperfections inherent in Higher-Order Ambisonics, which result in blurred sound localization and reduced listening area size, especially in environments with significant wall reflections.
Innovation Solution
A multiple-input multiple-output (MIMO) system employing a multiple error least mean square (MELMS) algorithm for adaptive filter design, which includes psychoacoustic constraints like pre-ringing and post-ringing to optimize loudspeaker arrangements and filter responses, ensuring effective sound zone generation and crosstalk cancellation even in environments with limited loudspeaker placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large number of loudspeakers are used for spatial sound field reproduction, then sound quality and spatial reproduction accuracy are improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an adaptive filter system as an intermediary component between the audio signal and the loudspeakers. This filter system compensates for the imperfections caused by using fewer loudspeakers by dynamically adjusting filter coefficients to correct spatial reproduction errors, effectively mediating between the limited hardware and the desired high-quality spatial sound reproduction.
Solution Approach 2:
The patent employs adaptive filtering by dynamically changing filter parameters (coefficients) based on measured acoustic characteristics of the listening environment. This allows the system to optimize spatial reproduction quality without adding physical loudspeakers, as the parameter adjustment compensates for the reduced number of acoustic sources.
2Manufacturing precision
If Higher-Order Ambisonics is used for spatial sound reproduction, then sound field representation is improved, but localization focus becomes blurred and listening area is reduced
Solution Approach 1:
The patent implements a feedback mechanism where the actual acoustic response is measured using microphones in the listening environment, and this measurement is fed back to adjust the adaptive filter coefficients. This feedback loop corrects localization errors and maintains clear sound focus by continuously optimizing the reproduction based on real acoustic conditions.
Solution Approach 2:
The patent replaces the purely mathematical Higher-Order Ambisonics representation system with a hybrid approach that incorporates physical acoustic measurements and adaptive filtering. This substitution of the purely theoretical model with a physically-measured and adaptively-adjusted system resolves the localization blur by accounting for actual acoustic propagation characteristics.
3Manufacturing precision
If wave field synthesis is used for spatial sound reproduction, then sound field detail is improved, but the system becomes sensitive to wall reflections and requires extensive acoustic treatment
Solution Approach 1:
The patent converts the harmful effect of wall reflections into a beneficial feature by measuring the actual acoustic response including reflections and using this information to adjust the adaptive filters. Instead of treating reflections as errors to be eliminated, the system incorporates them into the overall acoustic characterization, allowing the system to work effectively in typical rooms without extensive acoustic treatment.
Solution Approach 2:
The system performs self-service by automatically measuring its own acoustic response in the listening environment and using this information to self-adjust the filter coefficients. This self-characterization and self-optimization capability allows the system to compensate for wall reflections and acoustic imperfections without requiring external acoustic treatment or manual calibration.
4Manufacturing precision
If adaptive filtering is applied to compensate for acoustic imperfections, then sound quality is improved, but computational complexity increases
Solution Approach 1:
The patent applies partial adaptive filtering by using a limited number of filter coefficients and focusing the adaptation on the most critical acoustic errors. Rather than attempting to perfectly compensate for all possible acoustic imperfections, the system uses a practical subset of filtering that provides sufficient quality improvement without excessive computational burden.
Data Source
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AI summary
A system and method include filtering with controllable transfer functions in signal paths upstream of K ≥ 1 output paths and downstream of Q ≥ 1 source input paths, and controlling with filter control signals of the controllable transfer functions according to an adaptive control algorithm based on error signals on M ≥ 1 error input paths and source input signals on the Q source input paths. The system and method further include at least one loudspeaker-room-microphone constraint.