Hearing Aid Compressor Control for Lower Modulation Distortion
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Solution Overview
Problem
Dynamic-range compression in hearing aids introduces audible compression modulation distortion due to rapid gain variations, which is exacerbated by block processing and discontinuous gain changes, making it difficult to balance distortion reduction with quick response to sound level increases.
Innovation Solution
Adaptive attack and release time constants are adjusted based on the difference between the input signal's power spectrum and the average signal spectrum, using longer times for small signal fluctuations and shorter times for large increases, ensuring reduced modulation distortion without compromising rapid gain reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If longer attack and release times are used, then compression modulation distortion is reduced, but compression overshoot increases and response to sudden sound level increases is slowed
Solution Approach 1:
The patent applies dynamics by making the attack and release time constants variable rather than fixed. The time constants adapt dynamically based on the input signal characteristics - using longer times for steady signals to reduce distortion and shorter times for rapidly changing signals to maintain fast response. This is implemented through monitoring the signal level changes and adjusting the time constants accordingly in different operational modes.
Solution Approach 2:
The patent changes the parameters (attack and release time constants) based on the operating conditions. By detecting the input signal level and its rate of change, the system selects appropriate time constant values from a set of predefined values, thereby optimizing the balance between distortion reduction and response speed for different signal types.
2Speed
If shorter attack and release times are used, then response to sudden sound level increases is improved, but compression modulation distortion increases
Solution Approach 1:
The system dynamically adjusts the time constants based on the instantaneous signal characteristics. When rapid signal changes are detected, shorter time constants are applied to ensure fast response. When signals are steady or slowly varying, longer time constants are used to minimize modulation distortion, thus optimizing performance for different signal conditions.
Solution Approach 2:
The patent implements parameter changes by selecting from multiple attack and release time constant values based on the input signal analysis. The system monitors signal level changes and switches between different time constant settings to match the signal characteristics, thereby reducing distortion during steady states while maintaining fast response during transient events.
3Productivity
If gain changes occur at block processing boundaries, then block processing efficiency is maintained, but discontinuities in gain values create distortion
Solution Approach 1:
The patent applies preliminary action by preparing and smoothing the gain values before they are applied at block boundaries. The gain evolution is calculated in advance and interpolated across block boundaries to ensure continuity, preventing the discontinuities that would otherwise cause distortion while maintaining block processing efficiency.
Data Source
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AI summary
The present invention relates to a hearing aid comprising a microphone for conversion of sound into an input audiosignal, a signal processor for processing the input audiosignal, the signal processor including a compressor, a receiver for conversion of the processed signal into sound, and wherein the compressor adapts the attack and release time constants in response to input signal fluctuations or variations whereby compression modulation distortion is reduced without noticeably affecting the syllabic compressor behavior for speech.