ANR Circuit Dynamic Filter Adjustment for Power and Noise
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Solution Overview
Problem
Existing personal active noise reduction (ANR) devices face issues with high power consumption, limited frequency range effectiveness, and the generation of unpleasant noise, often creating more noise than they reduce.
Innovation Solution
An ANR circuit employing buffers to configure settings synchronously with digital data transfer, incorporating ADC, DAC, digital filters, and variable gain amplifiers to alternately use different settings and store failsafe configurations, and a compression controller to manage feedforward and feedback noise based on acoustic energy thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ANR devices use continuous digital filtering and signal processing to reduce noise across frequency ranges, then noise reduction effectiveness is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic adjustment of digital filter characteristics based on detected noise characteristics. The system continuously monitors the acoustic environment and adapts filter coefficients, cutoff frequencies, and processing parameters in real-time to match the actual noise profile, thereby maintaining effective noise reduction while minimizing power consumption by avoiding unnecessary processing of quiet or steady-state conditions
Solution Approach 2:
The system changes multiple parameters including digital filter coefficients, cutoff frequencies, processing gain, and activation thresholds based on the detected noise spectrum and intensity. By adjusting these parameters dynamically rather than operating at fixed settings, the system optimizes the balance between noise reduction performance and computational power requirements
2Adaptability or versatility
If ANR devices process audio signals through multiple digital filters and pathways, then the range of audible frequencies for noise reduction is improved, but device complexity increases
Solution Approach 1:
The patent divides the audio signal processing into separate pathways: a feedforward pathway that processes external noise before it enters the earcup, and a feedback pathway that processes noise inside the earcup. Each pathway has dedicated digital filters optimized for its specific function, allowing independent optimization of each processing chain while maintaining overall system manageability
Solution Approach 2:
The system processes audio signals in both the time domain and frequency domain simultaneously using different filter types (FIR, IIR, adaptive filters) operating in parallel pathways. This multi-dimensional processing approach enables comprehensive frequency range coverage while organizing complexity into manageable functional blocks
3Reliability
If ANR devices increase processing gain and compression thresholds, then noise reduction intensity is improved, but unpleasant ANR-originated sounds are generated
Solution Approach 1:
The patent employs feedback microphones inside the earcup to monitor the actual acoustic environment and the output of the ANR system. This feedback is used to continuously adjust filter coefficients and processing parameters, detecting and correcting unwanted artifacts such as distortion, pumping effects, or resonance that may arise from aggressive noise reduction processing
Solution Approach 2:
The system applies compression and filtering at different levels across multiple pathways rather than using a single aggressive processing stage. By distributing the noise reduction function across multiple milder processing stages in the feedforward and feedback pathways, the system achieves effective noise reduction while avoiding the distortion and unpleasant artifacts that result from excessive single-stage processing
Data Source
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AI summary
An ANR device comprising: an acoustic driver; an ANR circuit coupled to the acoustic driver to operate the acoustic driver to acoustically output ANR anti-noise sounds to provide ANR adjacent an ear of a user across a range of frequencies having a lower and an upper limit; and a digital filter of the ANR circuit, wherein: the digital filter is configurable with a plurality of coefficients to implement an ANR transform to derive the ANR anti-noise sounds from ANR reference noise sounds; the ANR circuit is configured to repeatedly reconfigure the digital filter with different pluralities of coefficient values at a first recurring interval to reduce the provision of ANR at one of the limits without reducing a magnitude at which the ANR is provided across the entire range of frequencies in response to an event adversely affecting the provision of ANR at the one of the limits; and the ANR circuit is configured to repeatedly reconfigure the digital filter with different pluralities of coefficient values at a second recurring interval to reverse the reduction in the provision of ANR at the one of the limits in response to the event adversely affecting the provision of ANR at the one of the limits having ceased.