Hearing Input Gain Control for ADC Clipping and Pumping Reduction
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Solution Overview
Problem
Existing digital hearing devices face challenges in maintaining high signal quality due to dynamic range limitations and power consumption constraints, leading to issues like clipping and audible distortion from gain adjustments.
Innovation Solution
A hearing device with simultaneous fast and slow gain reduction mechanisms, utilizing a peak-level detector and sound-environment detector to control gain adjustments, reducing clipping and distortion by synchronizing fast and slow gain changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the dynamic range of the ADC is reduced to lower power consumption, then power consumption decreases, but the dynamic range becomes insufficient to handle loud acoustic signals without clipping
Solution Approach 1:
The patent implements dynamic gain control where the preamplifier gain is adjusted in real-time based on the detected signal level. When loud signals are detected, the gain is reduced to prevent clipping; when quiet signals are detected, the gain is increased to maximize the use of the ADC's limited dynamic range. This dynamic adaptation allows the system to maintain high signal quality across varying input levels while keeping the ADC's power consumption low.
Solution Approach 2:
The patent changes the operating parameters of the preamplifier by varying its gain setting according to the input signal characteristics. The system monitors the signal level and adjusts the preamplifier gain parameter accordingly, transforming a static system into one that adapts its parameters to maintain optimal performance under different conditions.
2Reliability
If the preamplifier gain is reduced to prevent clipping, then clipping is prevented, but the gain reduction produces audible distortion of the digitised signal
Solution Approach 1:
The patent uses a peak-level detector to monitor the incoming signal and predict when clipping might occur. By detecting peak levels in advance, the system can proactively adjust the preamplifier gain before clipping actually happens, preventing the harmful effect while maintaining signal integrity throughout the transition.
Solution Approach 2:
The system implements a feedback mechanism where the output of the peak-level detector is fed back to control the preamplifier gain. This closed-loop control allows the system to continuously monitor signal levels and make real-time adjustments to prevent clipping while minimizing audible distortion through smooth gain transitions.
3Reliability
If fast attack and release times are used for gain reduction, then clipping is prevented during transients, but the gain changes produce audible distortion and pumping effects
Solution Approach 1:
The patent segments the gain control function into two distinct pathways: a fast attack path for preventing clipping during transients, and a slower release path for returning to normal gain levels. This segmentation allows each pathway to be optimized independently - the attack path responds quickly to prevent clipping while the release path manages the transition back smoothly to minimize audible artifacts.
Solution Approach 2:
The system dynamically switches between different time constants for attack and release phases. During transient events, fast attack time constants are applied to quickly reduce gain and prevent clipping. During release phases, slower time constants are used to gradually return to normal gain levels, avoiding abrupt changes that would cause pumping effects.
Data Source
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AI summary
In digital hearing devices (1), it is common to use an ADC (5) which has a dynamic range only nearly large enough to comprise the dynamic range of typically encountered acoustic signals. A reduction of the preamplifier gain (G, G1, G2) thus needs to be applied when very loud signals are received in order to avoid clipping. It is known to temporarily reduce the preamplifier gain (G, G1) with fast attack and release times when a clipping of the input signal (M, AT, A) in the digitiser (5) is expected. The invention aims at improving the perceived signal quality of the audible signal provided to the user of the hearing device (1). This is achieved by simultaneously providing relatively fast and relatively slow temporary reductions of the amplifier gain (G, G1, G2) such that the slow gain reductions reduce the occurrences of fast gain reductions. This allows the hearing device (1) to provide a high quality sound to the user where clipping is reduced due to the fast gain reductions and where signal artefacts, such as pumping and switching noise, produced by the fast gain reductions is reduced due to the slow gain reductions.