Adaptive Noise Cancellation Biasing for Distance Compensation
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Solution Overview
Problem
Traditional adaptive noise cancellation systems in personal audio devices degrade as the distance between the error microphone and the listener's eardrum increases, due to a decrease in the gain of the transfer function, leading to reduced noise cancellation performance.
Innovation Solution
A personal audio device with a transducer, reference microphone, error microphone, and processing circuit that includes an adaptive filter, secondary path estimate filter, biasing portion, and coefficient control block to generate and scale an anti-noise signal, adapting to minimize ambient noise based on the difference between error and secondary path estimate signals, and correcting for the electro-acoustic path using a scaling factor between 0 and 1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the distance between the error microphone and the listener's eardrum increases, then the device can be held at varying pressures against the ear, but the noise cancellation performance degrades due to decreased gain of the transfer function
Solution Approach 1:
The system dynamically adjusts the anti-noise signal based on the detected distance between the error microphone and the listener's eardrum. The biasing portion modifies the anti-noise level in real-time to compensate for changes in transfer function gain, allowing the device to maintain effective noise cancellation across varying pressures and distances.
Solution Approach 2:
The patent changes the parameter of anti-noise signal level by applying a distance-dependent bias. The biasing portion adjusts the amplitude or gain of the anti-noise signal based on the measured distance, effectively compensating for the decreased transfer function gain that occurs at larger distances between the error microphone and eardrum.
2Device complexity
If traditional adaptive noise cancellation is used without distance compensation, then the system structure remains simple, but the noise cancellation effectiveness decreases at larger distances
Solution Approach 1:
The system performs preliminary distance detection and bias calculation before generating the final anti-noise signal. The biasing portion pre-adjusts the anti-noise level based on the detected distance, ensuring that the compensation is already in place before the noise cancellation signal is applied, which maintains effectiveness without requiring complex real-time adjustments.
3Reliability
If the error microphone is positioned closer to the transducer, then the transfer function gain is higher, but the device cannot accommodate varying pressure conditions
Solution Approach 1:
The system uses feedback from distance detection to continuously monitor and adjust the anti-noise signal level. By measuring the actual distance between the error microphone and eardrum, the biasing portion can compensate for variations in transfer function gain, allowing the system to maintain high effectiveness regardless of the microphone's fixed position or pressure conditions.
Data Source
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AI summary
A processing circuit may comprise an adaptive filter having a response generating an antinoise signal from a reference microphone signal, a secondary path estimate filter modeling an electroacoustic path of a source audio signal, a biasing portion that generates a scaled antinoise signal by applying a scaling factor and the response of the secondary path estimate filter to the antinoise signal, and a coefficient control block that shapes the response of the adaptive filter in conformity with the reference microphone signal and a modified playback corrected error signal by adapting the response of the adaptive filter to minimize ambient audio sounds in the error microphone signal, wherein the playback corrected error is based on a difference between the error microphone signal and source audio signal and the modified playback corrected error signal is based on a difference between the playback corrected error signal and scaled antinoise signal.