Hearing Normalization System with FFT-Based Dynamic Gain Control
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Solution Overview
Problem
Current hearing aids fail to accurately restore normal hearing frequency range and intensity, particularly in noisy environments, due to reliance on pure tone measurements that do not reflect real-world sound harmonic structures, leading to unnatural sound and poor fidelity.
Innovation Solution
A hearing normalization and correction system that uses shaped noise and broadband masking noise to measure actual hearing responses at various sound pressure levels, allowing for dynamic correction and automatic tuning based on precise frequency adjustments, thereby providing accurate and natural sound reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiband compression is used to adapt hearing aid settings to different sound pressure levels, then the hearing aid can adjust gain dynamically, but compression threshold settings are based on guesswork assumptions leading to incorrect frequency gain and unnatural sound
Solution Approach 1:
The patent replaces the mechanical/empirical tuning process with a digital signal processing system that uses Fast Fourier Transform (FFT) to analyze the spectral content of incoming audio signals. This substitution allows the system to automatically identify which frequency bands require compression based on actual signal characteristics rather than fixed thresholds, thereby resolving the contradiction between adaptability and measurement precision.
Solution Approach 2:
The system continuously monitors the spectral content of the input signal and uses this feedback to dynamically adjust compression thresholds and gain settings. The FFT analysis provides real-time feedback about which frequency bands exceed compression thresholds, allowing the system to adapt precisely to the actual acoustic environment and signal characteristics, eliminating guesswork from the tuning process.
2Speed
If fast acting compression is used to respond quickly to loud signals, then the hearing aid can reduce gain rapidly, but compressor gain overshoot occurs causing audible artifacts
Solution Approach 1:
The patent divides the audio spectrum into multiple frequency bands using FFT analysis and applies compression independently to each band. This segmentation allows the system to control compression dynamics on a per-band basis, preventing overshoot artifacts that would affect the entire frequency spectrum. Each band can be compressed at its optimal rate without causing artifacts in other bands.
Solution Approach 2:
The system dynamically adjusts compression parameters including threshold, ratio, and attack/release times based on the spectral content and energy distribution across different frequency bands. This dynamic adaptation allows fast compression where needed while preventing overshoot artifacts through band-specific parameter control, resolving the contradiction between speed and artifact generation.
3Speed
If release time is decreased to improve tracking of soft signals after loud signals, then the hearing aid can recover gain faster, but distortion artifacts increase reducing speech clarity
Solution Approach 1:
The patent applies separate release time constants to different frequency bands based on their individual characteristics and energy levels. This segmentation allows soft signals in bands that need fast recovery to receive quick gain restoration, while bands prone to distortion artifacts maintain longer release times to prevent them, thereby resolving the contradiction between recovery speed and artifact generation.
Solution Approach 2:
The system implements local quality control by assigning different release time parameters to different frequency bands according to their specific requirements. Bands with high energy or prone to distortion receive longer release times, while bands needing fast recovery receive shorter release times, optimizing both speech clarity and gain recovery speed simultaneously.
4Ease of operation
If hearing aid tuning is based on pure tone threshold measurements, then the tuning process is simplified, but the measurements do not accurately reflect low level hearing for persons with hearing impairment
Solution Approach 1:
The patent replaces the traditional pure tone threshold measurement methodology with an automated spectral analysis system using FFT. This substitution maintains ease of operation through automatic processing while dramatically improving measurement precision by analyzing the actual spectral content and energy distribution of hearing responses across multiple frequency bands, providing accurate low-level hearing assessment.
5Adaptability or versatility
If the audio spectrum is divided into multiple frequency bands for compression, then dynamic range compression can be applied, but the frequency relationship of phonetic spectral energy in speech is greatly altered
Solution Approach 1:
The system dynamically adjusts the spectral balance and frequency weighting in each band to preserve the natural phonetic spectral energy relationships in speech. The FFT-based analysis allows real-time detection and preservation of speech formants and spectral contours, ensuring that dynamic compression enhances speech intelligibility without altering the fundamental frequency relationships that carry phonetic information.
Data Source
AI summary
A hearing normalization and correction system and process provides accurate correction for users with mild to moderate hearing loss by using actual measured hearing response at multiple sound pressure levels. User measured hearing data is collected at considerably higher resolution and accuracy at multiple sound pressure levels and is automatically converted to multiple accurate correction responses. Dynamic adaptive cross-fade response correction is used to deliver hearing normalization at varying sound pressure levels. Adaptive release response allows the hearing normalization system to accurately track the envelope of the incoming audio signal providing greatly enhanced accuracy and transparency. Adaptive headroom control is also applied to increase both input and output headroom providing professional dynamic range performance. The hearing normalization and correction system delivers audio fidelity and performance transcending that of normal hearing aid technology.