Hearing Aid Compression Using Modulation Spectrum Filtering
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Solution Overview
Problem
Existing dynamic compression methods in hearing aids and audio devices suffer from distortions due to non-linear processes and inertia in control systems, making it difficult to achieve real-time compression with minimal distortion, especially at high modulation frequencies.
Innovation Solution
The method involves determining and modifying the modulation spectrum of an audio signal using a predetermined compression function, allowing for selective compression in individual frequency channels, and employing coherent demodulation and instantaneous frequency determination to prevent phase information loss and reduce computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional dynamic compression is performed with fast control time constants, then the compression responds quickly to signal changes, but audible distortions occur and sound quality deteriorates
Solution Approach 1:
The patent implements dynamic control time constants that adapt to the modulation frequency of the input signal. For high modulation frequencies, slower control time constants are used to prevent distortions, while for low modulation frequencies, faster control time constants can be applied. This dynamic adaptation resolves the contradiction between fast response and distortion prevention.
Solution Approach 2:
The control time constant parameter is changed based on the detected modulation frequency. The system measures the modulation frequency and adjusts the control time constant accordingly, transforming a fixed parameter into a variable one that optimizes performance across different signal conditions.
2Object-generated harmful factors
If slow control is used to prevent distortions, then sound quality is improved, but the effective compression decreases with increasing modulation frequency due to control system inertia
Solution Approach 1:
By making the control time constant dynamic and adaptive to modulation frequency, the system achieves fast effective compression for low frequency signals while using slower constants for high frequency signals to prevent distortions. This resolves the contradiction between maintaining high compression effectiveness and preventing distortions across different modulation frequencies.
3Productivity
If dynamic compression is performed in the time or frequency range of the audio signal, then compression is achieved, but phase information is lost and computational complexity increases
Solution Approach 1:
The patent performs compression in the modulation spectrum domain rather than directly in the time or frequency domain of the audio signal. By transforming the problem to the modulation spectrum through coherent demodulation, the system achieves compression while preserving phase information and reducing computational complexity compared to traditional approaches.
Data Source
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AI summary
Dynamic compression in hearing devices, and especially in hearing aids, should be distortion-free and practically in real time. To achieve this, it is proposed to derive the modulation spectrum (MS) from the audio or input signal. This modulation spectrum is then directly modified according to a predetermined compression function (KP). Finally, a modified or compressed output signal is recovered from the modified modulation spectrum. Alternatively, a complex envelope can be derived from the input signal and filtered using time-varying modulation filtering according to a predefined compression formula. A distortion-free, compressed output signal can also be recovered from this.