Adaptive Feedback Cancellation in Hearing Devices
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Solution Overview
Problem
Current hearing devices face challenges in effectively managing acoustic feedback, particularly in dynamic environments, leading to unwanted artifacts like entrainment and modulation, which compromise sound quality, especially with tonal components.
Innovation Solution
The method involves selectively enabling adaptive feedback cancellation only when the feedback path is changing, and disabling it when static, along with controlling frequency shifting to minimize artifacts, using a feedback canceller unit with an adaptive filter and a frequency shift unit, and employing a probe signal to model the feedback path accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If adaptive feedback cancellation is continuously enabled to compensate for feedback path changes, then feedback compensation accuracy is improved, but unwanted artifacts like entrainment and modulation are introduced that compromise sound quality
Solution Approach 1:
The system dynamically adjusts the adaptation state of the feedback canceller based on real-time detection of feedback path changes. The adaptive filter transitions between frozen and adaptive states, enabling feedback compensation only when actually needed rather than continuously operating. This dynamic control eliminates unwanted artifacts while maintaining compensation accuracy when feedback path changes are detected.
Solution Approach 2:
The system uses a feedback mechanism where the feedback path change detector continuously monitors for changes in the acoustic feedback path. When changes are detected, the system activates adaptive feedback cancellation; when no changes are present, the system freezes the adaptation. This feedback-controlled adaptation strategy ensures compensation accuracy is maintained only when necessary, avoiding artifact generation during static conditions.
2Reliability
If adaptive feedback cancellation is enabled to track feedback path changes, then feedback compensation is improved, but computational resources and processing time are increased
Solution Approach 1:
The system employs periodic monitoring of the feedback path using a detector that continuously checks for changes. Rather than continuously adapting the filter coefficients, the system periodically activates adaptation only when changes are detected. This periodic action approach maintains compensation reliability while significantly reducing computational processing time compared to continuous adaptation.
Solution Approach 2:
The feedback path change detector performs preliminary detection of feedback path changes before activating the adaptive feedback cancellation. This preliminary action allows the system to prepare for potential adaptation needs without continuously executing computationally intensive filter updates, thereby maintaining reliability while minimizing processing time consumption.
3Object-generated harmful factors
If frequency shifting is applied to reduce entrainment artifacts, then sound quality is improved, but additional processing complexity is introduced
Solution Approach 1:
The system extracts and removes the frequency shifting operation from the continuous signal processing chain, applying it only when entrainment artifacts are detected. By taking out this additional processing step and applying it conditionally rather than continuously, the system reduces sound quality degradation from entrainment artifacts while minimizing the added processing complexity to only when necessary.
Data Source
AI summary
This invention relates to a method of managing adaptive feedback cancellation in a hearing device comprising at least a microphone (1); a receiver (2); and a signal processing circuitry, configured to receive from said microphone (1) an input signal (Xtd, Xfd, Xc) and to provide said receiver (2) with an output signal (Yfd, Ufd, Utd). An external acoustic feedback path (300) defined by feedback sound (fb) traveling from the receiver (2) to the microphone (1) is represented by an external feedback path transfer function (3). The signal processing unit comprises at least a gain unit (4); a feedback canceller unit (5) comprising an adaptive filter element (6) configured to adaptively accommodate changes in said external acoustic feedback path transfer function (3); and a frequency shift unit (7) configured to stabilize an adaptation of the feedback canceler unit (5). The method according to the present invention comprises the steps of: estimating the external acoustic feedback path transfer function (3) by modeling/deriving a first estimated feedback path transfer function (8) to reflect the external acoustic feedback path transfer function (3), by said feedback canceler unit (5); compensating the input signal of the hearing device (Xfd), based on the first estimated feedback path transfer function (8), thereby generating a compensated input signal (Xc); providing at least part of the signal processing unit with the compensated input signal (Xc). The method further comprises the steps of: generating a probe signal (W), by an adaptation control block (9, 10); injecting the probe signal (W) into the output signal (Yfd) of the hearing device and letting the probe signal (W) be fed back to the microphone (1) through the external acoustic feedback path (300); modeling/deriving at least a reference estimated feedback path transfer function (11), based on a relation between the input signal (Xfd) and the probe signal (w); comparing said at least a reference estimated feedback path transfer function (11) with said first estimated feedback path transfer function (8), by a comparison unit (12) of said adaptation control block (9); and controlling the adaptive filter element (6) and the frequency shift unit (7) based on a comparison between such at least a reference estimated feedback path transfer function (11) and the first estimated feedback path transfer function (8).