Hearing Aid Feedback Suppression with Model Gain Estimation

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Solution Overview

Problem

Hearing aids with linear designs face challenges in managing acoustic feedback, particularly at high frequencies, leading to instability and compromised speech intelligibility, as they provide uniform gain across all input levels and often assume a single feedback frequency, which is rarely true in practice.

Innovation Solution

A hearing aid with an adaptive feedback suppression filter and a model gain estimator that determines the upper processor gain limit by comparing the level of the electrical output signal to the feedback cancellation signal, allowing for time-varying gain adjustments without monitoring loop gain or filter coefficients, thereby preventing feedback howling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of information

If gain is increased to improve speech intelligibility, then speech intelligibility is improved, but acoustic feedback becomes audible causing instability

Engineering Contradiction:

Improvespeech intelligibilityVSAvoidsystem stability

Core Design Contradiction:

Loss of informationVSReliability

Solution Approach 1:

The patent implements an adaptive feedback suppression filter that continuously monitors the acoustic feedback path and generates a cancellation signal to counteract the feedback. This feedback mechanism allows the system to maintain high gain for speech intelligibility while actively suppressing audible feedback through real-time adaptation of filter coefficients based on the measured feedback path characteristics

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically adjusts the gain parameters across different frequency bands and input levels using compression processing. By changing the gain parameters adaptively rather than using fixed linear gain, the system can provide sufficient gain for speech intelligibility while staying below the feedback threshold through non-linear compression that reduces gain at higher output levels

Inventive Principle:

Principle #35Parameter changes

2Reliability

If high frequency gain is increased to compensate for hearing loss, then hearing aid effectiveness is improved, but feedback risk increases due to less attenuation at high frequencies

Engineering Contradiction:

Improvehearing aid effectivenessVSAvoidfeedback risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies different gain characteristics to different frequency bands, providing high gain where needed for hearing loss compensation while applying compression and feedback suppression specifically targeted at frequencies prone to feedback. The adaptive filter independently processes different frequency components, allowing local optimization of gain and feedback suppression for each frequency region

Inventive Principle:

Principle #3Local quality

3Device complexity

If uniform gain is applied across all input levels, then device simplicity is maintained, but feedback constraint affects soft and medium-level sounds equally reducing speech intelligibility

Engineering Contradiction:

Improvedevice simplicityVSAvoidspeech intelligibility at various input levels

Core Design Contradiction:

Device complexityVSLoss of information

Solution Approach 1:

The patent transitions from static linear gain to dynamic non-linear compression processing that adapts gain based on input signal level. The compression processor dynamically adjusts the gain applied to different frequency bands based on the instantaneous signal level, providing high gain for soft sounds while controlling feedback at higher levels through level-dependent gain reduction

Inventive Principle:

Principle #15Dynamics

4Object-affected harmful factors

If narrow-band gain reduction is applied to suppress feedback at a specific frequency, then feedback at that frequency is reduced, but the assumption of single feedback frequency is rarely true causing feedback to shift to other frequencies

Engineering Contradiction:

Improvefeedback suppression at specific frequencyVSAvoidhandling multiple feedback frequencies

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The patent divides the frequency spectrum into multiple bands and applies independent feedback suppression and compression processing to each band. The adaptive feedback filter operates across the full frequency range with multiple coefficients that can independently suppress feedback at different frequencies simultaneously, rather than treating feedback as a single frequency phenomenon

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The adaptive feedback suppression filter continuously monitors the actual feedback occurring in the system and dynamically adjusts its transfer function to cancel feedback at whatever frequencies are currently problematic. This feedback-driven adaptation allows the system to track and suppress multiple feedback frequencies as they occur in reality, rather than relying on predetermined single-frequency suppression

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8019104B2Hearing aid with feedback model gain estimation

Publication Date: 2011.09.13 WIDEX AS

AI summary

A hearing aid includes an input transducer for transforming an acoustic input signal into an electrical input signal, a processor for generating an electrical output signal by amplifying the electrical input signal with a processor gain, an output transducer for transforming the electrical output signal into an acoustic output signal, an adaptive feedback suppression filter for generating a feedback cancellation signal, and a model gain estimator generating an upper processor gain limit and for providing a control parameter indicating a possible misadjustment of the model.