Rearview Mirror Microphone Array for Vehicle Noise Reduction
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Solution Overview
Problem
Existing noise reduction systems for vehicular microphones face challenges in effectively canceling noise in the presence of the rearview mirror and other surfaces, leading to poor speech intelligibility and increased dynamic range issues, especially in hands-free automotive systems where microphones are distant from the audio source.
Innovation Solution
A space-time noise reduction system using multiple microphones positioned within the rearview mirror assembly, employing angular processing techniques like the Bryson-Schwetz-Turnbull algorithm and space-time adaptive beamforming to generate a low noise reference signal, which adjusts gain based on the cross-product angle and compression ratio, and incorporates a delay and sum beamformer to improve speech quality and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If digital signal processing techniques are used to reduce vehicular noise, then noise attenuation is improved, but delay and time variation are introduced that disrupt single-microphone systems
Solution Approach 1:
The patent introduces a reference microphone positioned to capture only noise (not speech) as an intermediary signal source. This reference noise signal serves as a mediator that allows the system to identify and subtract noise components from the primary microphone signal without requiring complex digital signal processing that would introduce delay. The reference microphone acts as a physical intermediary that captures the noise field separately, enabling cleaner noise cancellation.
2Object-affected harmful factors
If microphones are positioned in tandem (front and back) for noise cancellation, then noise subtraction capability is improved, but the rearview mirror requires a deeper housing which increases design complexity
Solution Approach 1:
The patent transitions from a tandem microphone arrangement (requiring depth in one dimension) to a distributed array configuration where microphones are positioned across multiple dimensions within the available mirror housing space. By utilizing lateral and vertical spacing rather than purely depth-based separation, the system achieves noise cancellation capability without requiring excessive housing depth, thus resolving the contradiction between noise cancellation performance and housing design constraints.
3Adaptability or versatility
If microphones are used at a distance from the audio source in hands-free systems, then installation flexibility is improved, but speech-to-noise ratio deteriorates and dynamic range increases
Solution Approach 1:
The patent segments the audio capture function across multiple microphones positioned at different locations within the mirror assembly. Rather than relying on a single distant microphone, the system divides the capture task among several microphones, each contributing to different aspects of the audio signal. This segmentation allows the system to maintain installation flexibility while improving the overall speech-to-noise ratio through spatial diversity and subsequent signal combining.
Solution Approach 2:
The patent merges signals from multiple microphones positioned at different locations and orientations within the mirror assembly. By combining these spatially distributed signals through adaptive processing, the system achieves an effective speech-to-noise ratio comparable to close-microphone systems while maintaining the installation flexibility of distant microphone placement. The merging of multiple spatial perspectives compensates for the distance-related signal degradation.
4Object-affected harmful factors
If standard noise reduction algorithms are used to lower noise content, then noise attenuation is improved, but speech intelligibility does not necessarily improve and significant speech content may be removed as noise
Solution Approach 1:
The patent uses a reference microphone as an intermediary that captures a clean noise signal without speech content. This reference signal serves as a template for identifying noise components in the primary microphone signal. By comparing the primary signal against this noise template, the system can selectively attenuate noise while preserving speech components, avoiding the problem of standard algorithms misidentifying and removing significant speech content as noise.
Solution Approach 2:
The patent implements a feedback mechanism where the reference noise signal continuously informs the noise cancellation process. The system uses the reference microphone's output to adaptively adjust noise subtraction parameters in real-time, providing feedback about the current noise environment. This feedback loop enables the system to distinguish between noise and speech more accurately, preventing the removal of significant speech content while maintaining effective noise attenuation.
Data Source
AI summary
A space-time adaptive beamformer for reducing noise in a vehicle that includes two or more microphones. A first weighting network is used for adjusting the signal characteristics of at least one output of the microphones while at least one delay network is also used for delaying the output in time of at least one output of the microphones. A second weighting network then adjusts the signal characteristics of the output of each of the delay networks and at sum adder works to combine the output of the first weighting network and the second weighting network. Finally, an output of the sum adder is combined with an artificial noise free reference signal to provide a low distortion noise reduced output. By generating a desired signal that acts as an artificial noise free signal reference, adequate noise reduction to be obtained without the distortion created due to processing non-linearity.