Implanted Microphone Gain Control for Vibration-Induced Feedback
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Solution Overview
Problem
Implantable hearing instruments with implanted microphones face issues of vibration sensitivity, leading to distortion and feedback from body sounds and the wearer's own voice, which existing methods struggle to address without affecting sound sensitivity or introducing noise.
Innovation Solution
An automatic gain control (AGC) circuit is implemented to selectively adjust the gain of signals based on their magnitude and frequency content, reducing the amplification of unnaturally large vibrations while preserving desired sound signals, and mapping the microphone's dynamic range into the signal processor's range to prevent clipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the microphone gain is increased to improve sensitivity to airborne sound, then the sensitivity to vibration increases, but body sounds and feedback cause saturation and distortion
Solution Approach 1:
The signal processing is segmented into multiple stages: initial amplification stage, detection stage for large signals, and attenuation stage. The system divides the dynamic range handling into different functional blocks that operate sequentially based on signal level, allowing high gain for small signals while providing protection against saturation from large vibration signals
Solution Approach 2:
The system performs preliminary detection of signal magnitude before full amplification occurs. The detector circuit monitors the amplified signal level and triggers attenuation preemptively when large signals are detected, preventing saturation before it occurs. This preliminary action allows the system to maintain high gain settings while being protected against harmful vibrations
2Object-affected harmful factors
If methods are used to reduce vibration sensitivity, then feedback and distortion are reduced, but sound sensitivity may be affected and noise may be introduced
Solution Approach 1:
The attenuation factor is dynamically adjusted based on the detected signal magnitude. The system transitions from high gain mode (for normal sound levels) to attenuation mode (when large vibration signals are detected). This dynamic adjustment ensures that sound sensitivity is preserved during normal operation while vibration sensitivity is reduced only when necessary, preventing both saturation and unnecessary noise introduction
Solution Approach 2:
The system changes the gain parameter conditionally based on signal level detection. When the detector identifies signals exceeding a predetermined threshold, the attenuation factor is applied to reduce the gain for subsequent processing. This parameter change is reversible and adaptive, allowing the system to maintain optimal sound sensitivity while reducing harmful vibration effects only when detected
3Stability of the object's composition
If the dynamic range of the microphone is mapped to the signal processor range, then clipping is prevented, but the signal-to-noise ratio may be degraded
Solution Approach 1:
The system extracts and handles large vibration signals separately from the normal audio signal path. By detecting and attenuating only the harmful large-magnitude signals while leaving normal sound signals unchanged, the system prevents clipping of the dynamic range without degrading the signal-to-noise ratio for useful audio content. The attenuation is selectively applied only when necessary
Data Source
AI summary
A method for use in an implantable hearing instrument, including receiving an output signal from an implanted microphone implanted in a person, identifying a first characteristic of said output signal, based on said first characteristic, amplifying said microphone output signal by at least one of a plurality of gain settings to produce an amplified signal, wherein said plurality of gain setting comprise at least two different gain settings, inputting said amplified signal into a signal processor, processing said amplified signal to generate a transducer drive signal; and using said transducer drive signal to drive implanted auditory stimulation device implanted in a person to stimulate an auditory component.