In-the-canal Hearing Aid Feedback Control

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Solution Overview

Problem

Hearing aid systems face challenges in minimizing acoustic feedback-induced oscillations due to sudden changes in the acoustic feedback path, such as when using cellular phones or hats, as existing adaptive feedback cancellation techniques struggle to adapt quickly enough to prevent feedback oscillations while maintaining sound quality.

Innovation Solution

A hearing aid system with a secondary sound responsive transducer in the ear canal detects impedance changes and adjusts the adaptation speed of the adaptive feedback cancellation filter to rapidly adapt to sudden changes in the acoustic feedback path, using a digital processor to compare output signals from both transducers and adjust the adaptation coefficients.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the adaptive feedback cancellation filter adapts quickly to sudden changes in the acoustic feedback path, then feedback oscillations are prevented, but voice and tonal signal quality is degraded

Engineering Contradiction:

Improvefeedback oscillation preventionVSAvoidsignal quality degradation

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent implements dynamic adaptation speed control by adjusting the adaptation rate of the feedback cancellation filter based on detected changes in the acoustic feedback path. When sudden changes are detected (indicating potential feedback oscillations), the filter adapts quickly; during stable conditions, the filter adapts slowly to preserve signal quality. This dynamic adjustment resolves the contradiction between fast adaptation for reliability and slow adaptation for signal quality.

Inventive Principle:

Principle #15Dynamics

2Speed

If the adaptation speed of the feedback cancellation filter is increased, then the filter responds faster to sudden changes in the acoustic feedback path, but correlation between input and output signals increases causing erroneous feedback signal estimation

Engineering Contradiction:

Improveadaptation speedVSAvoidfeedback signal estimation accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The system dynamically adjusts the adaptation speed based on the stability of the acoustic feedback path. During sudden changes, fast adaptation is enabled to capture new feedback characteristics. During stable periods, slow adaptation is used to maintain accurate feedback signal estimation by reducing correlation effects. This temporal separation of adaptation speeds resolves the contradiction between speed and measurement precision.

Inventive Principle:

Principle #15Dynamics

3Measurement precision

If a time delay is introduced into the processing loop to reduce correlation, then feedback signal estimation accuracy improves, but noticeable delay artifacts appear in the output

Engineering Contradiction:

Improvefeedback signal estimation accuracyVSAvoidaudible delay

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

Instead of using a fixed time delay, the patent employs adaptive filtering with dynamically adjusted adaptation speed. The filter processes signals in real-time without introducing fixed delays, while the adaptation rate is adjusted based on feedback path stability. This approach maintains measurement precision through adaptive adjustment without creating audible delay artifacts.

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively reduces acoustic feedback-induced oscillations by allowing the adaptive filter to quickly adapt to dynamic changes, preventing annoying whistling and maintaining high-quality sound output.

Implementation Method 1

a primary, or first, sound responsive transducer (e.g., a microphone)... additionally employs a secondary, or second, sound responsive transducer mounted in the user's open ear canal

Methodology Applied

Scientific EffectAcoustic detection: Sound

Implementation Method 2

a sound producing transducer (e.g., speaker) mounted in a user's open ear canal

Methodology Applied

Scientific EffectElectroacoustic transduction:

Data Source

PatentUS8655001B1In-the-canal hearing aid using two microphones

Publication Date: 2014.02.18 ADVANCED BIONICS AG

AI summary

A method and apparatus for enhancing the performance of an in-the-canal hearing aid by temporarily increasing the adaptation speed of an adaptive feedback cancellation filter in response to sudden changes in the acoustic feedback path. The hearing aid employs a sound producing transducer (e.g., a speaker) mounted in a user's open ear canal along with a sound responsive transducer (e.g., a microphone) and a second sound responsive transducer also mounted in the ear canal and spaced a fixed distance from the first sound responsive transducer. The output signals from the first and second sound responsive transducers are applied to a digital processor which compares the respective output signals to detect impedance changes in the audio feedback path. The detected occurrence of an impedance change is then used to influence the adaptation speed of the adaptive feedback cancellation filter.