Bidirectional Microphone Array Beamforming for Echo Rejection
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Solution Overview
Problem
Bidirectional microphones in teleconference devices face challenges with echo rejection due to proximity effects and polarity conflicts when used in close proximity to speakers, leading to cancellation of meaningful signals during gain sharing/mixing.
Innovation Solution
The use of beamforming and gainsharing mixing techniques with small circular arrays of bidirectional microphones to resolve polarity conflicts and optimize echo rejection, including the formation of audio beams and selection of perpendicular beam pairs based on audio source direction to combine signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If bidirectional microphones are used in teleconference devices with speakers placed close to each other, then echo rejection is improved, but signal cancellation occurs during gain sharing/mixing due to polarity conflicts
Solution Approach 1:
The patent segments the audio signal processing by creating multiple beamforming channels (first beam, second beam, third beam, fourth beam) from the bidirectional microphones. Each channel processes signals with different polarity configurations, allowing the system to selectively combine signals that reinforce rather than cancel each other, thus maintaining reliability while achieving echo rejection.
Solution Approach 2:
The patent changes the polarity parameter of the audio signals by inverting the polarity of signals from certain bidirectional microphones before mixing. This parameter change resolves the polarity conflict that causes signal cancellation, allowing meaningful signals to be preserved while maintaining the echo rejection benefits of bidirectional microphones.
2Adaptability or versatility
If conventional gain sharing/mixing is used with bidirectional microphones, then coverage of the room with multiple talkers is achieved, but performance deteriorates due to polarity-induced signal cancellation
Solution Approach 1:
The patent implements dynamic beam selection and polarity adjustment based on the spatial location of audio sources. The system dynamically determines which beams to combine and adjusts polarities in real-time based on the direction of arrival of speech signals, maintaining high audio signal accuracy across different room coverage scenarios with multiple talkers.
Solution Approach 2:
The patent uses feedback mechanisms to detect the polarity state of combined signals and adjusts the mixing configuration accordingly. By monitoring the output of beam combinations and detecting signal cancellation, the system feedback-controls the polarity inversion and beam selection to optimize audio signal accuracy while maintaining room coverage capability.
3Adaptability or versatility
If bidirectional microphones pick up sound from both ends with opposite polarity, then 360-degree audio capture is achieved, but meaningful signals are cancelled out during mixing
Solution Approach 1:
The patent introduces asymmetry in the signal processing by selectively inverting polarities of signals from specific bidirectional microphones based on their spatial orientation. This asymmetric treatment of otherwise symmetric bidirectional microphone signals prevents cancellation of meaningful signals while preserving 360-degree audio capture capability.
Solution Approach 2:
The patent adds a polarity dimension to the audio signal processing by creating multiple versions of signals with different polarity configurations (original and inverted). This additional dimension allows the system to select and combine signals that constructively interfere, preventing information loss while maintaining omnidirectional capture.
Data Source
AI summary
A device including an array of bidirectional microphones optimizes the echo rejection of the bidirectional microphones. The microphone array receives audio from an audio source and generates audio signals from each of the bidirectional microphones. The device forms audio beams from combinations of the audio signals generated from the microphone array. Each audio beam captures audio from either its positive polarity zone or its negative polarity zone. The device determines a direction of the audio source and selects a perpendicular audio beam pair based on the direction of the audio source. The perpendicular audio beam pair includes a primary audio beam aimed toward the direction of the audio source and a secondary beam perpendicular to the primary audio beam. The device generates an output signal by combining the primary audio beam with the secondary audio beam based on polarity zone the audio is captured for each audio beam.