Hearing Amplifier Gain Control for Clipping and Pumping Reduction
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Solution Overview
Problem
Existing digital hearing devices face challenges in maintaining high signal quality due to limitations in dynamic range and power consumption, leading to issues like clipping, distortion, and audible gain changes, particularly in environments with varying sound levels.
Innovation Solution
The implementation of a hearing device with simultaneous fast and slow gain reductions, controlled by a fast-working and slow-working gain controller, respectively, to manage dynamic range and reduce clipping while minimizing audible distortion, using a microphone, attenuator, preamplifier, digitizer, and signal processor with a peak-level detector and sound-environment detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the ADC dynamic range is reduced to lower power consumption, then power consumption is reduced, but the dynamic range becomes insufficient to handle loud acoustic signals without clipping
Solution Approach 1:
The preamplifier gain is made dynamically adjustable through automatic gain control that varies the gain based on the level of the microphone signal. This allows the system to adapt the dynamic range to match the actual signal levels, preventing clipping during loud signals while maintaining high gain for soft signals, thus resolving the contradiction between power consumption and signal quality.
Solution Approach 2:
The system changes the operating parameters of the preamplifier by adjusting its gain according to signal level. The automatic gain control modifies the preamplifier gain parameter dynamically, allowing the ADC to operate within its optimal dynamic range regardless of whether the input signals are loud or soft, thereby maintaining signal quality without increasing power consumption.
2Reliability
If the attack time is shortened to prevent clipping during transients, then clipping is reduced, but audible distortion and pumping effects increase due to fast gain changes
Solution Approach 1:
The automatic gain control is divided into two separate components: a fast-acting controller with short attack time to prevent clipping, and a slow-acting controller with longer attack time to minimize audible distortion. This segmentation allows each controller to optimize for its specific function, resolving the contradiction between clipping prevention and distortion reduction.
Solution Approach 2:
The slow-acting automatic gain control acts as an intermediary that smooths out the gain changes produced by the fast-acting controller. By introducing this intermediate stage with longer time constants, the system reduces the abruptness of gain changes while maintaining effective clipping protection, thereby reducing audible distortion and pumping effects.
3Object-generated harmful factors
If the release time is lengthened to reduce audible distortion from gain changes, then distortion is reduced, but pumping effects increase and speech following transients is delayed
Solution Approach 1:
The release time parameter is segmented between two controllers: the fast-acting controller has a short release time to quickly restore gain after transients, preventing pumping effects and maintaining fast response to speech. The slow-acting controller has a longer release time to smooth gain changes and reduce audible distortion. This segmentation resolves the contradiction between response speed and distortion reduction.
Solution Approach 2:
The slow-acting automatic gain control serves as an intermediary that moderates the release time characteristics. Its longer time constants smooth out rapid gain recoveries that would cause pumping, while the fast-acting controller maintains the necessary speed for speech response. This intermediate stage resolves the contradiction between fast response and distortion reduction.
Data Source
AI summary
In digital hearing devices, it is common to reduce the preamplifier gain when very loud signals are received in order to avoid clipping. It is known to temporarily reduce the preamplifier gain with fast attack and release times when a clipping of the input signal in the digitizer is expected. Perceived signal quality of the audible signal provided to the user of the hearing device is herein improved by simultaneously providing relatively fast and relatively slow temporary reductions of the amplifier gain such that the slow gain reductions reduce the occurrences of fast gain reductions. This allows the hearing device to provide a high quality sound to the user where clipping is reduced due to the fast gain reductions and where signal artifacts, such as pumping and switching noise, produced by the fast gain reductions is reduced due to the slow gain reductions.