Adaptive Cardioid Microphone Filtering for Wind and Proximity Noise
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Solution Overview
Problem
Cardioid microphones face challenges with wind noise and proximity gain, where equalizing low-frequency content to reduce wind noise also diminishes the microphone's response when wind is not present, and proximity gain affects sound quality when a user speaks close to the microphone.
Innovation Solution
An adaptive filtering system using paired omnidirectional microphones and an audio processor that combines and filters audio signals to create a cardioid output, employing an adaptive low pass filter and high frequency gain filter, with feedforward and feedback processing to adjust the filter frequencies and reduce wind noise and proximity gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If equalizing down the low-frequency content from the microphone signal, then wind noise is reduced, but the useful response of the microphone is reduced when wind is not present
Solution Approach 1:
The patent implements a dynamic adaptive filter that continuously adjusts the low-frequency equalization based on real-time wind detection. The system transitions from static equalization to dynamic control by monitoring microphone signals for wind characteristics and adjusting the filter parameters accordingly, allowing the microphone response to be preserved when wind is absent while reducing wind noise when present.
Solution Approach 2:
The system employs feedback mechanisms where the output of the adaptive filter is monitored and used to adjust the filter parameters. The patent uses the microphone signal itself as feedback to detect wind conditions and automatically adjusts the low-frequency content processing, creating a closed-loop system that adapts to changing environmental conditions without manual intervention.
2Measurement precision
If using cardioid microphone in close proximity to user, then voice capture is improved, but proximity gain causes bass-heavy sound
Solution Approach 1:
The patent applies local quality by implementing frequency-specific processing targeted at the low-frequency range affected by proximity gain. The adaptive filter selectively processes bass frequencies while leaving other frequency ranges untouched, allowing close-proximity voice capture to be maintained while correcting the bass-heavy sound characteristic through localized frequency management.
Solution Approach 2:
The system dynamically changes the equalization parameters based on detected proximity conditions. When a user is detected in close proximity, the adaptive filter automatically adjusts the low-frequency gain parameters to compensate for proximity gain effects, transitioning the frequency response characteristics in real-time based on the spatial relationship between microphone and speaker.
Data Source
AI summary
Cardioid adaptive filtering includes receiving a first and second audio signals from first and second omnidirectional microphones; combining the audio input signals into a cardioid signal; filtering the cardioid signal to create a first filtered output using an adaptive low pass filter controlled by a frequency control, the adaptive low pass filter having a controllable corner frequency f1; filtering the first filtered output, using a high frequency gain filter with a corner frequency f2, to create an equalized cardioid output signal; performing feedforward processing of the audio input signals to provide a wind feedforward signal; using the equalized cardioid output and the first or second audio input signal, performing proximity feedback to generate a proximity feedback signal; adjusting the frequency f1 of the adaptive low pass filter using the wind feedforward signal and the proximity feedback signal; and providing the equalized cardioid output signal for use in receiving captured audio.