Adaptive Feedback Cancellation in Sound Processing for Hearing Aids

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Solution Overview

Problem

Existing sound signal processing technologies in hearing aids face challenges in effectively reducing feedback loops, which cause audible whistling or howling, especially when high gain is applied, due to incomplete vent blocking leading to ear occlusion and reduced airflow, and existing methods like frequency translation introduce unwanted artefacts or fail to distinguish between source and feedback signals.

Innovation Solution

A sound processing device that includes a frequency transposition stage, amplification stage, feedback estimation stage, and phase inverting feedback cancelling stage, where the frequency transposition stage can be selectively activated or deactivated based on sound classification to improve feedback cancellation accuracy and reduce artefacts, with variable feedback estimation rates to enhance adaptation speed.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the ear mould vent is completely blocked to improve feedback problems, then feedback is reduced, but ear occlusion occurs resulting in changes to the sound of the wearer's own voice and preventing air flow needed for hygiene and comfort

Engineering Contradiction:

ImprovefeedbackVSAvoidear comfort and hygiene

Core Design Contradiction:

Object-affected harmful factorsVSEase of operation

Solution Approach 1:

The harmful feedback component is extracted and separated from the desired sound signal through adaptive filtering. The system identifies and removes only the feedback portion while preserving the original sound qualities and maintaining vent openness for comfort and hygiene.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

An adaptive feedback canceller acts as an intermediary between the microphone input and output, processing the signal to eliminate feedback paths while preserving the natural sound transmission through the open vent.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If gain is reduced over a wide range of frequencies to minimize feedback, then feedback is reduced, but the amplifier does not achieve the desired output level

Engineering Contradiction:

ImprovefeedbackVSAvoidoutput level

Core Design Contradiction:

Object-affected harmful factorsVSPower

Solution Approach 1:

The feedback cancellation is applied locally and selectively only at frequencies where feedback occurs, rather than reducing gain across the entire frequency spectrum. This preserves the desired output level while targeting feedback suppression precisely where needed.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system dynamically adjusts the feedback cancellation parameters based on detected feedback characteristics, modifying the filtering approach to maintain output levels while suppressing feedback when and where it occurs.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If frequency transposition is applied to stabilize the amplifier, then feedback oscillation is reduced, but unwanted artefacts are introduced which decrease the quality of the sound

Engineering Contradiction:

Improveamplifier stabilityVSAvoidsound quality

Core Design Contradiction:

Stability of the object's compositionVSManufacturing precision

Solution Approach 1:

The system extracts and removes feedback components directly from the signal path using adaptive filtering, avoiding the need for frequency transposition altogether. This maintains amplifier stability while preserving original sound quality without introducing transposition artefacts.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The mechanical approach of frequency transposition is replaced with a signal processing approach using adaptive feedback cancellation, achieving the same stability goal through a different mechanism that preserves sound fidelity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Object-affected harmful factors

If multiple tuneable notch filters are employed to handle feedback at several frequencies, then feedback cancellation is improved, but device complexity increases

Engineering Contradiction:

Improvefeedback cancellationVSAvoidnumber of filters

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

A single adaptive feedback canceller performs the function of multiple fixed notch filters by dynamically adjusting its filtering characteristics based on detected feedback frequencies. This single multi-functional device replaces what would otherwise require multiple separate filters.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The feedback cancellation system is made dynamic and adaptive, automatically adjusting its parameters to track and cancel feedback at varying frequencies, replacing the need for multiple static notch filters with one adaptable filter.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS20080279395A1Feedback Compensation in a Sound Processing Device

Publication Date: 2008.11.13 SONOVA AG

AI summary

There is disclosed a sound processing device (300) configured to apply a frequency shift to at least one frequency component of a received sound signal and to amplify at least part of the received sound signal. The processing device (300) is also adapted to generate an estimated feedback signal for combination with the received sound signal via a phase inverting feedback canceller (314). Associated methods (400, 600) of processing a sound signal are also disclosed.