ANR Hear-Through Instability Mitigation via Sensor-Based Gain Control
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Solution Overview
Problem
Active Noise Reduction (ANR) systems with aware mode are prone to unstable conditions due to high gain levels, leading to acoustic artifacts such as loud noises, squeals, or chirps, which can be uncomfortable for users.
Innovation Solution
The system employs a sensor-based approach to detect conditions likely to cause instability in the pass-through signal path, adjusting the variable gain associated with this path using a variable gain amplifier or by selecting filter coefficients, and disabling or enabling the pass-through signal path as necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high gain levels are used in the pass-through signal path to allow more ambient noise to reach the user, then the hear-through functionality is improved, but system stability deteriorates leading to acoustic artifacts
Solution Approach 1:
The patent applies dynamics by making the gain level adjustable rather than fixed. The system dynamically adapts the gain in the pass-through signal path based on detected stability conditions. When instability is detected (through sensors detecting acoustic artifacts or signal analysis), the gain is reduced or disabled. When stable conditions are detected, the gain is increased to improve hear-through functionality. This dynamic adjustment resolves the contradiction between maintaining high gain for versatility and low gain for stability.
2Device complexity
If sensor-based detection is used to detect instability conditions, then system complexity is reduced compared to signal processing solutions, but detection precision may be limited
Solution Approach 1:
The patent uses sensor-based detection as an intermediary method to detect instability conditions. Instead of directly analyzing the audio signal for instability (which would require complex signal processing), the system uses sensors to detect physical conditions correlated with instability, such as acoustic artifacts or environmental factors. This intermediary approach reduces computational complexity while providing sufficient detection capability for adjusting the gain level.
3Adaptability or versatility
If the pass-through signal path is enabled with high gain to improve ambient noise reproduction, then user awareness of environment is improved, but acoustic artifacts such as loud noises and squeals occur
Solution Approach 1:
The patent implements feedback by continuously monitoring the system for instability conditions and adjusting the gain accordingly. Sensors detect acoustic artifacts or other indicators of instability in the pass-through signal path, and this feedback is used to automatically reduce or disable the gain. This closed-loop feedback mechanism prevents acoustic artifacts from occurring while still allowing ambient noise reproduction when conditions are stable, resolving the contradiction between improving ambient noise reproduction and eliminating harmful acoustic artifacts.
Data Source
AI summary
In one aspect a method that includes receiving an input signal captured by one or more first sensors associated with an active noise reduction (ANR) device, and processing the input signal using a first filter disposed in an ANR signal path to generate a first signal for an acoustic transducer of the ANR device. The input signal is processed in a pass-through signal path disposed in parallel with the ANR signal path to generate a second signal for the acoustic transducer, wherein the pass-through signal path allows a portion of the input signal to pass through to the acoustic transducer in accordance with a variable gain. One or more second sensors detect an existence of a condition likely to cause instability in the pass-through signal path, and in response, the variable gain is adjusted. A driver signal for the acoustic transducer is generated using an output based on the adjusted gain.