Adaptive Virtual Microphone for Earbud ANC
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Solution Overview
Problem
Existing active noise control (ANC) systems in wearable audio output devices struggle to effectively minimize unwanted ambient noise at the eardrum due to mismatches in acoustic path transfer functions between the error microphone and the eardrum, especially when the earphone is loosely worn.
Innovation Solution
The ANC operation estimates the attenuation of noise at the eardrum based on a model of the acoustic relationship between the error microphone and the eardrum, and compensates for the mismatch in transfer functions by applying a bias to the adaptive filter of the feed forward loop, effectively optimizing noise cancellation at the eardrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ANC operations optimize attenuation of ambient noise at the error microphone, then noise cancellation performance at the microphone is improved, but the noise actually heard by the wearer at the eardrum is not minimized due to acoustic path mismatch
Solution Approach 1:
The patent introduces a virtual microphone as an intermediary that bridges the error microphone and the eardrum. The virtual microphone's output is derived from the error microphone signal but is designed to represent the acoustic conditions at the eardrum, thereby mediating between the measurement point and the target cancellation point
Solution Approach 2:
The patent changes the parameters of the error microphone signal by applying transfer function compensation and bias terms. This transforms the raw error signal into a compensated signal that accounts for acoustic path differences, effectively changing the signal characteristics to match eardrum conditions
2Ease of operation
If the earphone is loosely worn to increase comfort, then ease of operation is improved, but the mismatch of acoustic path transfer functions between anti-noise and leaked ambient noise increases, significantly affecting ANC performance
Solution Approach 1:
The patent implements dynamic adaptation by continuously adjusting the bias term based on the estimated acoustic path transfer function. This allows the ANC system to adapt to changing wear conditions (loose or tight fitting) in real-time, maintaining performance consistency despite variations in earphone placement
Solution Approach 2:
The patent uses feedback from the error microphone to estimate the acoustic path transfer function and dynamically adjust the bias term. This feedback mechanism enables the system to compensate for changes in acoustic conditions caused by loose or tight wearing, maintaining reliable ANC performance
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 allows for improved noise cancellation at the eardrum, reducing the ambient noise heard by the wearer and enhancing the overall listening experience by minimizing the discrepancy between noise cancellation at the error microphone and the eardrum.
Implementation Method 1
ANC aims to cancel the unwanted ambient noise by adaptively controlling an anti-noise signal driven from a speaker of the earphone so that the anti-noise signal may destructively interfere with the unwanted noise as detected by an error microphone
Implementation Method 2
due to the acoustic pressure drop across a housing mesh between the error microphone and the eardrum used to protect the earphone against environmental ingress
Data Source
AI summary
Disclosed are systems and methods for adaptive noise cancellation (ANC) at a virtual microphone located at the eardrum of a wearer of an earphone. The techniques estimate the level of leakiness of ambient noise in the earphone from the magnitude of the gain of the transfer function of the feed forward loop filter of the ANC. Based on the estimated leakiness, the techniques estimate the transfer function of the feed forward loop filter to compensate for the difference in the effect of noise cancellation at the virtual microphone and error microphone. A bias term that represents the difference in the frequency response of the attenuated noise at the virtual and error microphone may be added to the adaptive feed forward algorithm. The ANC operation may apply the bias term to the adaptive feed forward loop filter to reduce the ambient noise at the eardrum rather than at the error microphone.