Microphone Array Signal Processing for Omnidirectional Noise Reduction
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Solution Overview
Problem
Listening devices with directional algorithms face challenges in reducing noise floor while maintaining omnidirectional characteristics, as adding multiple microphone signals to reduce noise often results in loss of true omnidirectional response.
Innovation Solution
The use of two or more microphone units with a signal processing device that introduces a phase mismatch and amplitude mismatch to the signals, utilizing a FIR filter to modify the microphone signals and ensure equal representation of signals from different directions, effectively canceling directional behavior and achieving a 3 dB improvement in signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple microphone signals are added to reduce noise floor, then noise reduction is improved, but omnidirectional characteristic is lost
Solution Approach 1:
The patent applies parameter changes by introducing frequency-dependent scaling factors and phase shifts to the microphone signals. The scaling factor varies with frequency to compensate for the directional response that naturally emerges when adding multiple microphone signals. This allows the system to maintain omnidirectional characteristics across the audio spectrum while still achieving noise floor reduction through signal addition.
Solution Approach 2:
The patent implements dynamics by making the signal processing parameters adaptive rather than static. The scaling factors and phase shifts are adjusted based on frequency, allowing the system to dynamically maintain omnidirectional response across different frequency ranges. This dynamic adjustment ensures that the noise reduction benefit is preserved while the directional artifacts are compensated for in real-time.
2Measurement precision
If microphone signals are added to reduce noise, then signal-to-noise ratio is improved, but directional behavior is introduced
Solution Approach 1:
The patent uses parameter changes to counteract the directional behavior introduced by signal addition. By applying frequency-dependent scaling factors and phase shifts, the system modifies the parameters of the combined signal to flatten the directional response. This ensures that sounds from different directions are represented equally in the output, eliminating the artificial directional patterns that would otherwise appear when multiple microphone signals are combined.
3Object-affected harmful factors
If phase and amplitude adjustments are made to maintain omnidirectional response, then signal processing complexity is increased, but noise floor reduction is achieved
Solution Approach 1:
The patent manages complexity by using systematic parameter changes based on frequency. Rather than implementing complex adaptive algorithms, the solution applies predetermined scaling factors and phase shifts that are functions of frequency. This approach achieves noise floor reduction while maintaining omnidirectional response through relatively simple signal processing operations that can be efficiently implemented in real-time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces noise floor below that of single microphone units while preserving omnidirectional response, ensuring signals from all angles are equally attenuated, with minimal distortion and directionality, particularly effective in silent and noisy situations like wind noise.
Implementation Method 1
The directional behaviour is in fact due to phase cancellation caused by equality between the half-period of the acoustic signal and the distance between the microphone inlets
Data Source
AI summary
The invention regards a listening device with two or more microphone units. The listening device has a signal processing device and means for delivering a signal to the user of the device representative of the audio signals picked up by the microphones, whereby the signal processing device comprises means for adding and scaling the signals from at least two microphone units to provide a single added signal in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.