Adaptive Hearing Aid Compression 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 sudden sound level increases.
Innovation Solution
A hearing aid with an adaptive compressor that adjusts attack and release time constants based on input signal fluctuations and power spectrum differences, using longer times for small variations and shorter times for large increases to minimize modulation distortion while maintaining rapid gain reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If longer attack and release times are used to reduce audible distortion, 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 compressor adapts its time constants in real-time based on the characteristics of the input signal, switching between long time constants for stationary signals (to reduce distortion) and short time constants for transient signals (to maintain fast response). This dynamic adaptation resolves the contradiction by allowing the system to have both long and short time constants as needed.
Solution Approach 2:
The patent changes the parameters of the compressor (attack and release time constants) based on the input signal characteristics. By analyzing whether the input signal is stationary or transient and adjusting the time constants accordingly, the system optimizes performance for different signal types, reducing distortion for stationary signals while maintaining fast response for transients.
2Speed
If shorter attack and release times are used to maintain fast response to sudden sound level increases, then response speed is improved, but compression modulation distortion increases
Solution Approach 1:
The system dynamically adjusts the time constants based on signal characteristics. For transient signals requiring fast response, short time constants are used. For stationary signals where distortion is more problematic, long time constants are used. This dynamic behavior allows the system to optimize for speed when needed and minimize distortion when possible.
Solution Approach 2:
The attack and release time constants are changed as a function of the input signal characteristics. The compressor analyzes the signal to determine whether it is stationary or transient and adjusts the time constants accordingly, allowing fast response for transients while minimizing distortion for stationary signals.
3Device complexity
If gain changes occur discontinuously at block processing boundaries, then implementation is simpler, but distortion is generated due to periodic discontinuities
Solution Approach 1:
The patent ensures continuous gain changes across block processing boundaries by using overlapping windows and smooth transitions. Instead of allowing discontinuous jumps at block boundaries, the system maintains continuous modulation of the gain, eliminating periodic discontinuities and their associated distortion while keeping the implementation manageable through efficient windowing techniques.
Data Source
AI summary
A hearing aid includes a microphone for conversion of sound into an input audiosignal, a signal processor for processing the input audiosignal, the signal processor including a compressor, and a receiver for conversion of the processed signal into sound, wherein the compressor is configured to adapt attack and release time constants in response to input signal fluctuations.