ANR Signal Path Gain Control for Low-Frequency Overload
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Solution Overview
Problem
Active noise reduction (ANR) devices face overload conditions due to discrete acoustic signals or low-frequency pressure disturbances, leading to audible artifacts like oscillations, 'thuds,' and 'clicks' in small form-factor headphones, as they struggle to manage high displacement demands from transducers, causing objectionable user experiences.
Innovation Solution
Implementing a method that adjusts the gain of a variable gain amplifier (VGA) and selects coefficients for a tunable digital filter in the ANR signal flow path based on detected characteristics of the input signal, allowing selective throttling of compensation in specific frequency ranges to mitigate overload conditions without completely shutting off noise reduction, thereby reducing low-frequency noise modulations and improving user experience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ANR device attempts to compensate for low frequency pressure disturbances, then noise reduction performance is improved, but the transducer is driven to overload conditions causing audible artifacts
Solution Approach 1:
The patent implements dynamic adjustment of the feedforward compensator gain based on detected overload conditions. The gain is reduced when overload is detected and restored when overload subsides, allowing the system to adapt its compensation level in real-time to prevent artifacts while maintaining noise reduction performance when possible.
Solution Approach 2:
The system uses feedback from detecting overload conditions (such as transducer excursion limits or amplifier clipping) to control the feedforward compensator gain. This feedback loop allows the system to monitor its own performance and adjust parameters to prevent harmful artifacts from occurring.
2Object-affected harmful factors
If the feedforward compensator gain is reduced to prevent overload, then audible artifacts are minimized, but noise reduction performance deteriorates
Solution Approach 1:
The gain reduction is applied periodically or temporarily only when overload conditions are detected, rather than being continuously reduced. This allows the system to maintain full compensation performance during normal operation while briefly reducing gain only when necessary to prevent artifacts, minimizing the impact on overall noise reduction performance.
Solution Approach 2:
The gain is dynamically adjusted based on real-time detection of overload conditions, allowing the system to maintain high gain (and thus good noise reduction performance) during most operation while temporarily reducing gain only when overload occurs, optimizing the trade-off between performance and artifact prevention.
3Reliability
If the ANR device processes high amplitude low frequency signals, then compensation effectiveness is improved, but transducer displacement demands exceed capacity
Solution Approach 1:
The feedforward compensator gain is made dynamic rather than fixed, allowing it to be reduced when high amplitude low frequency signals cause transducer overload. This dynamic adjustment enables the system to maintain effective compensation when transducer capacity is available while preventing overload when displacement demands exceed capacity.
Solution Approach 2:
The system changes the gain parameter of the feedforward compensator in response to detected overload conditions. By adjusting this parameter, the system can reduce the compensation signal amplitude to match the transducer's displacement capacity while maintaining the compensatory function, thus preventing artifacts without completely disabling noise reduction.
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.