Microphone Noise Subtraction for Surface Contact Interference
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Solution Overview
Problem
Computing devices face noise interference from objects contacting their surfaces, such as styluses, which can significantly compete with desired sounds like human voices, due to vibrations being picked up by microphones, leading to distracting noise in recorded audio.
Innovation Solution
A microphone system comprising an environment microphone and a noise microphone, where the noise microphone is configured to primarily capture noise from objects contacting the device, allowing for noise estimation and subtraction from the environment microphone signal using adaptive filtering techniques, thereby reducing unwanted noise in the recorded sound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single microphone is used to capture desired sound, then the device complexity is low, but noise from objects contacting the device surface significantly interferes with the desired sound quality
Solution Approach 1:
The audio capture function is segmented into two specialized microphones: a first microphone optimized for capturing desired sound and a second microphone optimized for capturing noise. This segmentation allows each microphone to focus on its specific function, improving noise rejection while maintaining manageable system complexity through clear functional division.
Solution Approach 2:
The patent introduces an intermediary processing system that receives signals from both microphones, estimates noise characteristics from the second microphone, and subtracts the estimated noise from the first microphone's signal. This intermediary noise estimation and subtraction mechanism effectively reduces noise interference while preserving the desired sound quality.
2Object-affected harmful factors
If adaptive filtering is applied to reduce keyboard click noise, then noise reduction is achieved, but the filter length and processing complexity increase
Solution Approach 1:
The patent employs dynamic adaptive filtering where the filter characteristics are continuously adjusted based on real-time noise estimation from the second microphone. The filter length and coefficients are dynamically optimized to match the current noise conditions, achieving effective reduction of keyboard click noise and other surface contact noises while adapting to changing acoustic environments.
Solution Approach 2:
The system implements feedback mechanisms where the output from the noise estimation process is fed back into the adaptive filter to continuously refine noise cancellation. This feedback loop allows the system to learn and adapt to recurring noise patterns such as keyboard clicks, improving noise reduction effectiveness while maintaining computational efficiency through pattern recognition.
3Measurement precision
If the noise microphone is positioned close to the noise source, then noise capture is improved, but the desired sound is also more likely to be picked up
Solution Approach 1:
The patent applies local quality by positioning the second noise microphone in a specific location and orientation optimized for capturing noise from the device surface, while the first microphone is positioned and oriented for optimal desired sound capture. Each microphone has localized optimization for its specific function, allowing the noise microphone to be close to noise sources without significantly degrading desired sound capture since each mic has specialized positioning.
Solution Approach 2:
The system uses partial action by having the second microphone intentionally capture not only noise but also some desired sound, then using signal processing to separate and remove the noise component. The excessive capture of noise by the second microphone is acceptable because the subsequent noise estimation and subtraction process can isolate and remove the noise portion while preserving the desired sound from the first microphone.
Data Source
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AI summary
A computing device with a microphone system is disclosed. The computing device includes a microphone system with an environment microphone and a noise microphone. The environment microphone picks up an environment microphone signal which includes (1) a desired signal component based on desired sound and (2) a noise component based on noise from a noise source. The noise microphone picks up a noise microphone signal based on the noise, and is configured such that contributions to the noise microphone signal from the desired sound, if present, are attenuated relative to the environment microphone. A controller receives and processes time samples from the noise microphone signal to yield a noise estimation of the noise component. The estimation is subtracted from the environment microphone signal to yield and end-user output.