Adaptive ANR Digital Filter Loop Gain Matching
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Solution Overview
Problem
Existing active noise reduction (ANR) technologies face challenges in achieving optimal noise reduction performance while maintaining stability across different ear fits and individual ear acoustics.
Innovation Solution
The method involves receiving input signals from sensors associated with an ANR headphone, computing a frequency domain representation, and generating parameters for a digital filter to match a target loop gain, thereby adjusting the response of the filter across specific frequency ranges and second-order sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trade-off is made to achieve robust stability for any ear fit, then feedback loop stability is improved, but noise reduction performance deteriorates
Solution Approach 1:
The patent implements dynamic adaptation of ANR parameters based on detected ear fit characteristics. The system transitions from a static, one-size-fits-all stability approach to a dynamic system that adjusts filter parameters, gain, and bandwidth according to the specific user's ear canal geometry and acoustic properties. This allows each user to receive optimized noise reduction performance while maintaining stability through real-time parameter adaptation.
Solution Approach 2:
The system changes key ANR parameters including filter coefficients, loop gain, and bandwidth based on detected ear fit variations. By measuring acoustic characteristics of the user's ear and adjusting these parameters accordingly, the system resolves the contradiction by maintaining stability through controlled parameter changes while optimizing noise reduction performance for each individual user's anatomy.
2Manufacturing precision
If ANR parameters are optimized for individual ear acoustics, then noise reduction performance is improved, but system complexity increases
Solution Approach 1:
The system performs self-characterization by automatically measuring the acoustic properties of the user's ear canal and autonomously determining the optimal ANR parameters for that specific geometry. This self-service approach eliminates the need for manual fitting procedures or complex external calibration equipment, allowing the system to adapt to individual users while keeping the user interface simple and the overall system complexity manageable.
Solution Approach 2:
The system incorporates feedback mechanisms that continuously monitor acoustic characteristics and adjust ANR parameters accordingly. By using the ear canal's acoustic response as feedback to tune the adaptive filters and control loop parameters, the system achieves personalized optimization without requiring complex manual intervention, as the feedback loop automatically guides the parameter adaptation process.
3Manufacturing precision
If feedback loop gain is increased to improve noise reduction, then noise cancellation effectiveness is improved, but stability margin deteriorates
Solution Approach 1:
The system dynamically adjusts the feedback loop gain parameter based on the detected ear fit and acoustic characteristics. By changing the gain parameter adaptively rather than using a fixed high gain, the system achieves effective noise cancellation tailored to each user's anatomy while maintaining adequate stability margins through controlled gain adjustment based on real-time acoustic feedback.
Data Source
AI summary
A first input signal captured by one or more sensors associated with an ANR headphone is received. A frequency domain representation of the first input signal is computed for a set of discrete frequencies, based on which a set of parameters is generated for a digital filter disposed in an ANR signal flow path of the ANR headphone, the set of parameters being such that a loop gain of the ANR signal flow path substantially matches a target loop gain. Generating the set of parameters comprises: adjusting a response of the digital filter at frequencies (e.g., spanning between 200 Hz-5 kHz). A response of at least 3 second order sections of the digital filter is adjusted. A second input signal in the ANR signal flow path is processed using the generated set of parameters to generate an output signal for driving the electroacoustic transducer of the ANR headphone.