Hearing Device Adaptive Feedback Gain Control
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Solution Overview
Problem
Existing methods for determining maximum gain in hearing devices often require interruptions in normal operation, explicit measurements, discomfort due to high signal levels, and are not adaptable to changing feedback conditions, leading to suboptimal performance and susceptibility to environmental noise.
Innovation Solution
The method employs an adaptive filter to estimate the feedback transfer function using the LMS-algorithm, allowing continuous tracking of feedback stability during everyday use without interrupting normal operation, and automatically adjusts the gain to maintain stability, using preprocessing and conversion units to smooth coefficient fluctuations and determine maximum stable gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional feedback test methods (Direct Method, Negative-Slope Method, Open-Loop Identification, Closed-Loop Identification) are used to determine maximum gain, then feedback stability can be measured, but normal operation of the hearing device must be interrupted and explicit measurement actions are required
Solution Approach 1:
The hearing device automatically performs feedback stability measurements using its own operational signals without requiring external intervention or interruption. The system uses the acoustic feedback path during normal operation to continuously estimate maximum gain, eliminating the need for separate measurement procedures and allowing uninterrupted service.
Solution Approach 2:
The feedback stability measurement process is integrated into the continuous operation of the hearing device. Instead of interrupting normal function for discrete measurements, the system continuously estimates feedback characteristics using ongoing acoustic signals, maintaining both measurement capability and uninterrupted operation simultaneously.
2Measurement precision
If high signal levels are used during feedback testing to ensure accurate measurement, then measurement accuracy improves, but user comfort deteriorates due to perceived loudness
Solution Approach 1:
The system uses an intermediary processing approach where feedback characteristics are estimated through correlation analysis of existing acoustic signals rather than direct high-level probing. This intermediary method allows accurate feedback threshold determination using lower signal levels that do not cause user discomfort, avoiding the need for loud test signals while maintaining measurement precision.
Solution Approach 2:
The measurement approach changes from using high signal levels to utilizing correlation-based estimation with lower-level operational signals. By changing the measurement parameter from signal amplitude to correlation coefficient, the system achieves accurate feedback threshold determination without exposing the user to uncomfortable high sound levels.
3Device complexity
If fixed maximum gain values are set during initial fitting, then device configuration is simplified, but adaptability to changing feedback conditions (reduced ear shell fit, dirt accumulation) is lost
Solution Approach 1:
The system transitions from static fixed gain values to dynamic adaptive maximum gain determination. The feedback stability measurement is performed continuously or periodically to detect changes in feedback conditions such as ear shell fit degradation or dirt accumulation, allowing the device to automatically adapt gain settings to current conditions while maintaining simple initial configuration through automated adjustments.
Solution Approach 2:
The system implements a feedback mechanism where continuous or periodic measurement of feedback stability informs automatic adjustments to maximum gain settings. This closed-loop feedback allows the device to detect and adapt to changing conditions such as reduced ear shell fit or vent blockage, maintaining optimal performance without requiring manual reconfiguration.
4Measurement precision
If environmental noise is present during feedback testing, then measurement robustness is compromised, but adding longer averaging times and pseudo-noise techniques increases measurement complexity
Solution Approach 1:
The system uses correlation-based estimation that leverages the inherent structure of acoustic feedback signals to achieve robust measurements in noisy environments. By utilizing the self-correlation properties of feedback paths, the system obtains reliable feedback threshold estimates without requiring complex pseudo-noise sequences or extensive averaging procedures, maintaining measurement robustness while minimizing processing complexity.
Data Source
AI summary
A method for determining a maximum gain is disclosed that is applicable in a forward signal path starting at a microphone (1) and ending at a receiver (11) of a hearing device, the maximum gain being a gain value at which just no feedback occurs. The method comprising the steps of estimating a estimated feedback transfer function (F′) characterizing a feedback signal path (15) starting at a receiver (11) and ending at a microphone (1) of the hearing device, while the hearing device is inserted into an ear of a hearing device user, and adapting the estimated feedback transfer function (F′) as a result of a changing feedback signal path (15) by applying an adaptive algorithm. The invention is characterized by determining the maximum gain from the estimated feedback transfer function (F′), in particular by coefficients of the estimated feedback transfer function.