Motion-Sensed Hearing Feedback Cancellation for Stable Adaptive Filtering
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Solution Overview
Problem
Existing adaptive feedback cancellation algorithms in ear-wearable devices struggle with perturbations caused by user movements and environmental changes, leading to issues like chirping and howling, as they assume a stable feedback path and stationary input signal, which is often not met in practical scenarios.
Innovation Solution
Incorporating a motion sensor to detect feedback path changes and adjust the adaption speed of adaptive filters, using modes such as normalized least mean squared and signed NLMS algorithms, or combining filters with different step sizes to enhance robustness and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive feedback cancellation algorithms assume a stable feedback path and stationary input signal, then the algorithms can operate with simple fixed adaption rates, but the system becomes unstable and produces chirping and howling when user movements or environmental changes occur
Solution Approach 1:
The patent applies dynamics by making the adaption rate of the adaptive filter variable rather than fixed. The system dynamically adjusts the adaption rate based on detected feedback path changes, switching between a first adaption rate for stable conditions and a second adaption rate for changing conditions. This resolves the contradiction by allowing the system to maintain stability when the feedback path is stable while quickly adapting when changes occur, preventing chirping and howling.
Solution Approach 2:
The patent changes the parameter of adaption rate based on the state of the feedback path. When feedback path changes are detected (indicating user movement or environmental change), the system switches to a second adaption rate that is different from the first adaption rate used during stable periods. This parameter change allows the system to respond appropriately to different operational conditions, maintaining reliability while avoiding harmful artifacts.
2Adaptability or versatility
If the adaptive filter uses a fast adaption rate to quickly respond to feedback path changes, then the system can rapidly adapt to new conditions, but the system becomes sensitive to perturbations and produces chirping and howling
Solution Approach 1:
The system dynamically selects the adaption rate based on the detected state of the feedback path. During stable periods, a slower adaption rate is used to avoid sensitivity to perturbations. When feedback path changes are detected, the system switches to a faster adaption rate to quickly track the changes. This dynamic adjustment resolves the contradiction by providing fast adaptation only when necessary, while maintaining stability during normal operation.
Solution Approach 2:
The patent changes the adaption rate parameter based on feedback path stability. The system monitors for feedback path changes and switches between at least two different adaption rates: a first rate for stable conditions and a second rate for changing conditions. This parameter switching allows the system to achieve high adaptability when needed while avoiding the harmful effects of fast adaption during stable periods.
3Reliability
If the adaptive filter uses a slow adaption rate to maintain stability during stable periods, then the system avoids chirping and howling, but the system cannot quickly adapt when feedback path changes occur
Solution Approach 1:
The system dynamically adjusts the adaption rate based on the operational state. During stable periods, a slow adaption rate maintains reliability and avoids chirping and howling. When feedback path changes are detected, the system switches to a fast adaption rate to quickly adapt to new conditions. This dynamic behavior resolves the contradiction by providing both stability and rapid adaptability at different times as needed.
Solution Approach 2:
The patent implements parameter changes by switching between different adaption rates based on feedback path stability. The system uses a first adaption rate during stable periods to maintain reliability, and switches to a second adaption rate when changes are detected to achieve quick adaptation. This parameter switching strategy simultaneously achieves both stability and fast adaptability.
4Reliability
If the system continuously monitors for feedback path changes to adjust adaption rate, then the system can respond to movements and maintain stability, but the device complexity increases due to additional motion sensors and processing
Solution Approach 1:
The system uses the existing error signal from the feedback cancellation process itself to detect feedback path changes, rather than relying solely on external motion sensors. The error signal naturally contains information about feedback path stability, and the system processes this existing signal to determine when to switch adaption rates. This self-service approach reduces device complexity by utilizing already-available system signals.
Solution Approach 2:
The error signal from the feedback cancellation system serves multiple functions: it is used both for the feedback cancellation itself and for detecting feedback path changes to adjust the adaption rate. This multi-functionality reduces the need for separate dedicated motion detection circuitry, thereby reducing device complexity while maintaining the ability to respond to movements and environmental changes.
Data Source
AI summary
An audio input signal is digitized via circuitry of an ear-wearable device. An adaptive feedback canceller has an adaptive filter producing an output that is inserted into the digitized audio input signal to cancel feedback. A motion detector provides a motion signal indicative of motion of the car-wearable device. A processor is operable to determine a change in a feedback path based on the motion signal. The processor causes the adaptive filter to have faster adaption in response to the change in the feedback path is above a first threshold. The processor also causes the adaptive filter to have slower adaption in response to the change in the feedback path being below a second threshold.