ANR Signal Path Gain and Filter Tuning Under Overload
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Solution Overview
Problem
Active noise reduction (ANR) devices face challenges in managing overload conditions, particularly in small form-factor devices like in-ear headphones, where low frequency disturbances can cause audible artifacts and degrade user experience.
Innovation Solution
The method involves automatically adjusting the gain of a variable gain amplifier (VGA) and selecting coefficients for a tunable digital filter in the ANR signal flow path based on characteristics of the input signal, allowing for selective throttling of compensation in specific frequency ranges to mitigate overload conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gain of the variable gain amplifier is increased to improve noise reduction performance, then the noise reduction capability is enhanced, but the device becomes more susceptible to overload conditions causing audible artifacts
Solution Approach 1:
The patent implements dynamic gain adjustment by making the gain of the variable gain amplifier controllable and adjustable based on signal characteristics. The system automatically modifies the gain level in response to detected overload conditions, transforming a static amplification system into a dynamic one that adapts to prevent artifacts while maintaining noise reduction effectiveness.
Solution Approach 2:
The patent changes the gain parameter of the variable gain amplifier based on analyzed signal characteristics. By monitoring the input signal and determining when overload conditions are likely to occur, the system adjusts the gain parameter to an optimal level that prevents artifacts while preserving noise reduction performance.
2Object-affected harmful factors
If the compensation is throttled to mitigate overload conditions, then audible artifacts are reduced, but the noise reduction capability is degraded
Solution Approach 1:
The patent applies partial throttling of compensation by selectively reducing the gain only when and where overload conditions are detected, rather than uniformly reducing compensation across all frequency ranges and time periods. This partial action maintains noise reduction effectiveness in safe conditions while preventing artifacts only when necessary.
Solution Approach 2:
The system employs feedback mechanisms by analyzing the output signal characteristics and using this information to adjust the gain of the variable gain amplifier. The feedback loop continuously monitors for signs of overload and artifacts, then adjusts compensation levels accordingly to maintain optimal performance without excessive throttling.
3Adaptability or versatility
If the gain is adjusted frequently to adapt to changing signal conditions, then the adaptability to different environments is improved, but the device complexity increases
Solution Approach 1:
The patent performs preliminary analysis of the input signal characteristics before adjusting the gain, using predictive criteria to determine when overload conditions are likely to occur. This preliminary action allows the system to proactively adjust the gain to prevent artifacts rather than reactively adjusting after artifacts occur, reducing the frequency and complexity of adjustments needed.
Data Source
AI summary
The technology described in this document can be embodied in a method that includes receiving an input signal captured by one or more sensors associated with an active noise reduction (ANR) headphone, and determining one or more characteristics of a first portion of the input signal. Based on the one or more characteristics of the first portion of the input signal, a gain of a variable gain amplifier (VGA) disposed in an ANR signal flow path can be adjusted, and accordingly, a set of coefficients for a tunable digital filter disposed in the ANR signal flow path can be selected. The method further includes processing a second portion of the input signal in the ANR signal flow path using the adjusted gain and selected set of coefficients to generate a second output signal for the electroacoustic transducer of the ANR headphone.