SNR-Driven Compressive Amplification for Hearing Aids
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Solution Overview
Problem
Traditional compressive amplification systems in hearing aids degrade signal-to-noise ratio (SNR) in noisy environments and amplify noise in quiet environments, leading to suboptimal hearing experience for individuals with hearing impairments.
Innovation Solution
The SNR driven compressive amplification system (SNRCA) minimizes SNR degradation by dynamically adjusting compression ratios and gain based on local and global SNR estimates, applying reduced gain in low SNR environments, and using estimated level post-processing for linearization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If classic compressive amplification is applied to restore audibility for soft signals, then audibility is improved, but signal-to-noise ratio degrades in noisy environments
Solution Approach 1:
The patent implements dynamic compression ratios that adapt based on local SNR conditions. When local SNR is low (noisy environments), the compression ratio is reduced to minimize noise amplification. When local SNR is high (quiet environments), the full compression ratio is applied to restore audibility of soft signals. This dynamic adjustment resolves the contradiction by making the compression behavior conditional on the acoustic environment.
Solution Approach 2:
The patent applies different compression ratios to different frequency channels based on local SNR estimates for each channel. This allows the system to apply strong compression to frequency regions with good SNR (where speech is clear) while applying minimal or no compression to frequency regions with poor SNR (where noise dominates). This local differentiation resolves the contradiction by treating each frequency channel according to its specific noise conditions.
2Measurement precision
If classic compressive amplification applies gain independently of noise amount, then audibility for soft signals is restored, but undesired noise amplification occurs in pure noise environments
Solution Approach 1:
The system dynamically adjusts the compression ratio based on the detected noise level and local SNR. In pure noise environments where no speech is present, the local SNR is low, triggering a reduction of the compression ratio to minimal or zero levels. This prevents the amplification of noise while maintaining the capability to restore audibility when speech is present and SNR is high.
Solution Approach 2:
The patent employs a feedback mechanism where the local SNR is continuously estimated and used to control the compression ratio. The system monitors the acoustic environment, calculates local SNR for each frequency channel, and adjusts the compression parameters in real-time based on this feedback. This closed-loop control ensures that compression is applied only when beneficial (high SNR) and avoided when harmful (low SNR).
Data Source
Figure 1
Figure 2A~2C
Figure 2D~2E
AI summary
A hearing device, e.g. a hearing aid, comprises A) an input unit providing an electric input signal with a first dynamic range of levels comprising a target signal and/or a noise signal; B) an output unit providing output stimuli; C) a dynamic compressive amplification system comprising c1) a level detector unit providing a level estimate of the electric input signal; c2) a level post processing unit for providing a modified level estimate in dependence of a first control signal; c3) a level compression unit for providing a compressive amplification gain in dependence of the modified level estimate and a user's hearing data; and c4) a gain post processing unit for providing a modified compressive amplification gain in dependence of a second control signal; D) a control unit configured to provide a classification of said electric input signal, and to provide said first and second control signals based on said classification; and E) a forward gain unit for applying the modified compressive amplification gain to the electric input signal. A method of operating a hearing device is furthermore provided.