Adaptive Feedback Cancellation Step Size Control
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Solution Overview
Problem
Existing audio processing systems, such as hearing aids and public address systems, face instability due to acoustic feedback, which is difficult to predict and control, especially when the microphone and loudspeaker are closely positioned, leading to artifacts like howling.
Innovation Solution
A method to determine the system parameter of an adaptive algorithm, such as the step size in a feedback cancellation algorithm, by approximating the magnitude square value of the open loop transfer function (OLTF) using estimated impulse responses and beamformer filter responses, allowing for real-time prediction and control of feedback estimation without knowing the true feedback path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the microphone and loudspeaker are placed closely together to improve compactness, then the device size is reduced, but acoustic feedback increases causing system instability and howling artifacts
Solution Approach 1:
The patent implements feedback cancellation by continuously monitoring the acoustic feedback path from loudspeaker to microphone and generating an anti-phase signal to cancel the feedback. The system estimates the feedback path characteristics and subtracts the predicted feedback signal from the microphone input, allowing close placement of microphone and loudspeaker while maintaining system stability through active feedback compensation.
Solution Approach 2:
The patent introduces an adaptive filter as an intermediary component that models the acoustic feedback path. This filter acts as a mediator between the feedback source and the cancellation mechanism, allowing the system to predict and cancel feedback without requiring physical separation of the microphone and loudspeaker. The adaptive filter continuously updates its parameters to track changes in the acoustic environment.
2Reliability
If adaptive feedback cancellation is implemented to reduce feedback artifacts, then system stability is improved, but the complexity of the audio processing system increases
Solution Approach 1:
The patent employs self-service by using the system's own output signal as the reference input for the adaptive filter. The feedback cancellation system utilizes the loudspeaker output signal to predict and cancel the feedback path, eliminating the need for external calibration equipment or additional microphones. The system automatically adapts to changes in the acoustic environment using its existing signals.
Solution Approach 2:
The patent implements parameter changes through adaptive filtering, where the filter coefficients are continuously adjusted based on the observed feedback path characteristics. The system dynamically modifies its parameters (filter weights) to track changes in the acoustic environment, allowing it to maintain effectiveness without increasing hardware complexity. The adaptation is achieved through standard adaptive algorithms that modify numerical parameters rather than adding physical components.
3Speed
If the adaptation rate of the feedback cancellation algorithm is increased to respond faster to feedback changes, then the response speed is improved, but the risk of system instability and oscillations increases
Solution Approach 1:
The patent applies dynamics by making the step size parameter adaptive rather than fixed. The step size is adjusted dynamically based on the current state of the adaptive filter and the observed feedback characteristics. When the system is close to convergence or when feedback changes are minimal, the step size is reduced to prevent oscillations. When rapid adaptation is needed, the step size is increased appropriately. This dynamic adjustment allows the system to achieve fast response when needed while maintaining stability during normal operation.
Data Source
AI summary
A method and an audio processing system determine a system parameter, e.g. step size, in an adaptive algorithm, e.g. an adaptive feedback cancellation algorithm so as to provide an alternative scheme for feedback estimation in a multi-microphone audio processing system. A feedback part of the system's open loop transfer function is estimated and separated in a transient part and a steady state part, which can be used to control the adaptation rate of the adaptive feedback cancellation algorithm by adjusting the system parameter, e.g. step size parameter, of the algorithm when desired system properties, such as a steady state value or a convergence rate of the feedback, are given/desired. The method can be used for different adaptation algorithms such as LMS, NLMS, RLS, etc. in hearing aids, headsets, handsfree telephone systems, teleconferencing systems, public address systems, etc.