Transient Suppression Circuit for Hearing Aids
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Solution Overview
Problem
Hearing aid wearers often find transient sounds, such as those from slamming doors or dropping objects, unpleasant and annoying, despite these sounds not being loud enough to trigger output compression, highlighting a need to reduce their harshness without affecting intended sounds like speech and music.
Innovation Solution
An audio system with a transient suppression circuit that rectifies input signals, generates a threshold envelope, accumulates and normalizes the difference between the rectified signal and the threshold, and applies a calculated gain to suppress transient sounds, using a processing circuit with a rectifier, threshold envelope generator, accumulator, normalizer, and amplifier to achieve this.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If output compression limiting is applied to reduce transient sounds, then the harshness of transient sounds is reduced, but the intended sounds such as speech and music are also affected and reduced in volume
Solution Approach 1:
The patent applies different processing characteristics to different portions of the audio signal by detecting transient characteristics (sudden amplitude increases) and applying suppression only to those portions while leaving other portions unaffected. This local differentiation allows transient sounds to be reduced without affecting intended sounds like speech and music.
Solution Approach 2:
The system dynamically adjusts the gain applied to the audio signal based on real-time detection of transient characteristics. The gain calculation incorporates the accumulated difference between the rectified signal and threshold envelope, creating a time-varying gain that suppresses transients while preserving other sounds.
2Object-affected harmful factors
If a complex frequency-domain transient suppression algorithm is used, then the suppression of transient sounds is more effective, but the computational resources required exceed the capabilities of hearing aids with limited processing power
Solution Approach 1:
The patent replaces complex frequency-domain processing with a simpler time-domain approach. By using rectification, threshold envelope generation, and accumulation in the time domain, the system achieves transient suppression without requiring the substantial computational resources of frequency-domain methods, making it suitable for hearing aids.
Solution Approach 2:
The system changes the domain of processing from frequency-domain to time-domain, fundamentally altering the parameter space in which transient suppression is performed. This parameter change simplifies the computational requirements while maintaining suppression effectiveness.
Data Source
AI summary
An audio system includes a transient suppression circuit that rectifies an input signal representing target sounds and transient sounds and produces a threshold envelope of the rectified input signal. The transient suppression circuit accumulates the difference between the rectified input signal and the threshold envelope, and normalizes the accumulated difference using the rectified input signal. A gain is calculated using this normalized accumulated difference and applied to the input signal to suppress the transient sounds without substantially affecting the target sounds.