Microphone Array Filter Using Spatial Coherence for Diffuse Sound Extraction
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Solution Overview
Problem
Current multi-channel filters for extracting diffuse sound from microphone arrays are not optimal, leading to poor performance in capturing diffuse sound and suppressing direct sound, especially when multiple sources are active or transient signals are present, and they do not achieve a suitable directivity pattern for omnidirectional diffuse sound capture.
Innovation Solution
A novel multi-channel filter is proposed that uses a linear constraint based on spatial coherence between microphone signals to determine filter coefficients, minimizing a cost function while ensuring a distortionless constraint for diffuse sound, which captures diffuse sound without distortion and suppresses direct sound effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If current multi-channel filters are used for diffuse sound extraction, then direct sound suppression is achieved, but diffuse sound capture performance deteriorates and directivity pattern becomes unsuitable
Solution Approach 1:
The patent changes the fundamental parameter of the filter constraint from direct sound-based constraints to spatial coherence-based constraints. By using the spatial coherence matrix of the diffuse sound field, the filter adapts its parameters to preserve diffuse sound while suppressing direct sound, resolving the contradiction between suppression and capture performance
Solution Approach 2:
The patent replaces the traditional mechanical filter design approach with a statistical signal processing approach. Instead of using fixed filter structures, it employs statistical properties (spatial coherence) of the sound field to dynamically determine filter coefficients, enabling optimal performance for both diffuse sound capture and direct sound suppression
2Ease of operation
If conventional filters are used, then processing simplicity is maintained, but performance in capturing diffuse sound and suppressing direct sound deteriorates
Solution Approach 1:
The filter design is self-adapting by using the spatial coherence matrix that is inherently present in the microphone array measurements. The system uses its own measured data to automatically configure the optimal filter parameters without requiring external calibration or complex manual tuning, maintaining simplicity while improving reliability
3Object-generated harmful factors
If existing multi-channel filters are applied, then direct sound attenuation is achieved, but omnidirectional directivity pattern for diffuse sound is not obtained
Solution Approach 1:
The patent applies local quality by making the filter response direction-dependent based on the spatial coherence characteristics. The filter maintains high gain in all directions for diffuse sound (omnidirectional) while creating directional nulls specifically at the directions of arrival of direct sound components, achieving both omnidirectional capture and directional suppression
Data Source
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AI summary
A method comprises estimating a spatial coherence between a first diffuse sound portion in a first microphone signal and a second diffuse sound portion in a second microphone signal. The first microphone signal is captured by a first microphone and the second microphone signal is captured by a second microphone wh ich is spaced apart from the first microphone in a known manner. The method further comprises defining a linear constraint for filter coefficients of a diffuse sound filter, the linear constraint being based on the spatial coherence. The method also comprises calculating at least one of signal statistics and noise statistics over the first microphone signal and the second microphone signal. The method also comprises determining the filter coefficients of the diffuse sound filter by solving an optimization problem concerning at least one of the signal statistics and noise statistics while considering the linear constraint for the filter coefficients.