Hearing Aid Feedback Control Using Pre-Stored Candidate Paths
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Solution Overview
Problem
Adaptive filters in hearing devices take several hundreds of milliseconds to converge after a fast change in the acoustic feedback path, leading to system instability during this period.
Innovation Solution
A hearing aid with a feedback control system that uses an adaptive filter and a database of previously determined candidate feedback paths to quickly identify and adapt to changes in the feedback path, providing an updated estimate to stabilize the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If adaptive filters are used in feedback cancellation system, then feedback cancellation efficiency is improved, but system stability deteriorates during fast feedback path changes due to slow convergence
Solution Approach 1:
The system pre-stores multiple candidate feedback paths in a database before they are needed. When a feedback path change is detected, the system can immediately retrieve a pre-computed candidate path instead of waiting for the adaptive filter to converge, thus maintaining stability during transitions while preserving estimation accuracy when converged.
Solution Approach 2:
The system dynamically switches between different feedback path models based on convergence status. During normal operation, it uses the adaptive filter estimate; during fast changes before convergence, it switches to candidate paths from the database. This dynamic adaptation resolves the contradiction between needing accurate tracking and maintaining stability during transitions.
2Reliability
If adaptive filter convergence time is reduced, then system stability is improved during feedback path changes, but computational complexity increases
Solution Approach 1:
Candidate feedback paths are pre-computed and stored in a database before runtime. This shifts computational complexity from real-time operation to offline preparation, allowing fast response during transitions without increasing real-time processing demands or overall system complexity.
Solution Approach 2:
Instead of computing new feedback paths in real-time, the system creates and stores copies of candidate feedback paths in advance. During operation, it simply retrieves these pre-computed copies, avoiding complex real-time calculations while maintaining stability during fast changes.
3Loss of time
If database of candidate feedback paths is maintained, then convergence time is reduced, but memory requirements increase
Solution Approach 1:
The system pre-computes and stores candidate feedback paths in a database, transforming time requirements into storage requirements. This allows immediate retrieval during fast changes, reducing convergence time while the memory cost is managed through efficient storage of pre-computed data.
Solution Approach 2:
The system changes the state of feedback path data from dynamically computed to pre-stored. By transforming the parameter from real-time computation to stored retrieval, it reduces time loss during convergence while accepting increased memory requirements for storing candidate paths.
Data Source
AI summary
A hearing aid adapted for being worn by a user at or in an ear of the user comprises a) at least one input transducer for converting sound in an environment around the user to at least one electric input signal representing said sound; b) an output transducer for converting a processed output signal provided in dependence of said at least one electric input signal to stimuli perceivable to the user as sound; c) a feedback control system comprising an adaptive filer, the feedback control system being configured to provide an adaptively determined estimate (h*(n)) of a current feedback path (h(n)) from said output transducer to said at least one input transducer in dependence of c1) said at least one electric input signal, c2) said processed output signal, and c3) an adaptive algorithm. The hearing aid further comprises d) a database comprising a multitude (M) of previously determined candidate feedback paths (hm); and e) a controller configured to identify a change in the current feedback path (h(n)) based on the adaptively determined estimate (h*(n)) of the current feedback path and at least one of said multitude of previously determined candidate feedback paths (hm). A method of operating a hearing aid is further disclosed. The invention may e.g. be used in hearing aids, e.g. binaural hearing aid systems or headsets, or speakerphones, or combinations thereof.