Direction of Arrival Circuit for Microphone Noise Suppression
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Solution Overview
Problem
Existing noise suppression systems using single microphones struggle to effectively separate desired speech from noise, especially in harsh environments where noise and speech share the same frequency spectrum, and require more accurate determination of voice and direction of arrival.
Innovation Solution
A noise suppression system employing plural microphones, a fixed beam former, a blocking matrix, plural adaptive filters, and a direction of arrival circuit that prevents filters from adapting in the presence of a signal in the look direction, utilizing adjustable gain circuits and null-forming circuits to improve noise reduction and direction determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If adaptive filters are used for noise suppression, then noise reduction performance is improved, but filter adaptation may occur during desired speech presence causing speech distortion
Solution Approach 1:
The system uses direction of arrival detection as feedback to control adaptive filter adaptation. When a signal is detected in the look direction, the adaptive filters are prevented from adapting, thus avoiding speech distortion while maintaining noise suppression capability during speech presence
Solution Approach 2:
The system dynamically adjusts the adaptation state of the adaptive filters based on real-time direction of arrival detection. The filters switch between adaptation and non-adaptation modes depending on whether speech is present in the look direction, optimizing both noise reduction and speech preservation
2Reliability
If direction of arrival detection is used to control filter adaptation, then speech distortion is reduced, but system complexity increases
Solution Approach 1:
The system introduces a direction of arrival detector as an intermediary component that mediates between the adaptive filters and the input signals. This detector controls when the filters should adapt by detecting signals in the look direction, providing a systematic way to manage the trade-off between noise reduction and speech preservation
3Object-affected harmful factors
If null-forming circuits are used to enhance noise reduction, then noise suppression performance is improved, but direction of arrival estimation accuracy may be affected
Solution Approach 1:
The system segments the signal processing into distinct functional paths: one for direction of arrival estimation and another for noise suppression using null-forming circuits. This segmentation allows the direction of arrival detector to operate independently on the raw signals before null-forming, preserving estimation accuracy while enabling aggressive noise suppression in the filtered path
Data Source
AI summary
A noise suppression system includes plural microphones, a fixed beam former, a blocking matrix, plural adaptive filters, and a direction of arrival circuit coupled to the adaptive filters that prevents the filters from adapting in the presence of a signal in the look direction. The direction of arrival circuit causes the filters to adapt more quickly in the absence of a signal in the look direction. A pair of adjustable gain circuits is coupled to each microphone. A first adjustable gain circuit from each pair is calibrated during the presence of a desired signal and a second adjustable gain circuit from each pair is calibrated during the presence of an interfering signal. A fixed null-forming circuit is coupled to a first pair of variable gain circuits and an adaptive null forming circuit is coupled to a second pair of adjustable gain circuits. The ratio of the gains of the null forming circuits is used as a control signal. Successive ratios are averaged with a variable smoothing constant and a control signal is derived from the averaged ratios.