ANC Ear-Coupling Detection for Stable Personal Audio Noise Canceling
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Solution Overview
Problem
Personal audio devices, such as wireless telephones, face challenges in maintaining effective noise cancellation due to varying acoustic environments and inconsistent coupling between the output transducer and the user's ear, leading to suboptimal performance of adaptive noise canceling systems.
Innovation Solution
Incorporating an adaptive noise-canceling (ANC) processing circuit within the device that utilizes a reference microphone to measure ambient noise, an error microphone to assess the coupling quality, and a secondary path adaptive filter to adjust the anti-noise signal generation, ensuring effective noise cancellation by monitoring and responding to changes in ear pressure and transducer coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive noise canceling is used to improve noise cancellation performance, then noise cancellation effectiveness is improved, but the system performance becomes highly sensitive to coupling quality between transducer and ear
Solution Approach 1:
The patent employs feedback mechanisms by using an error microphone to continuously monitor the actual acoustic output at the user's ear and adjusting the anti-noise signal accordingly. The system measures the secondary path (acoustic transfer function) and uses this feedback to adaptively adjust the noise canceling algorithm, allowing it to compensate for variations in coupling quality and maintain reliable performance across different wearing conditions
Solution Approach 2:
The system dynamically adapts to changing coupling conditions by continuously estimating the secondary path and adjusting the adaptive filter coefficients in real-time. The noise canceling system transitions from a static configuration to a dynamic one that can respond to changes in ear coupling, device position, and acoustic environment, thereby maintaining performance consistency
2Ease of operation
If the transducer is loosely coupled to the ear, then comfort is improved, but noise cancellation performance deteriorates
Solution Approach 1:
The system dynamically adjusts the noise canceling strategy based on the detected coupling quality. When loose coupling is detected through secondary path estimation, the system adapts by adjusting the adaptive filter coefficients and potentially reducing the aggressiveness of the anti-noise signal, allowing comfortable wearing while maintaining acceptable noise cancellation performance
Solution Approach 2:
The system changes operational parameters based on coupling quality detection. By monitoring the secondary path characteristics and error microphone signal, the system modifies filter coefficients, gain settings, and adaptation rates to optimize performance for the current coupling condition, enabling reliable noise cancellation across a range of comfort levels
3Reliability
If the transducer is pressed hard against the ear, then noise cancellation performance is improved, but user comfort deteriorates
Solution Approach 1:
When tight coupling is detected through secondary path estimation, the system adjusts parameters such as reducing the adaptation rate of the adaptive filter, lowering the gain of the anti-noise signal, or switching to a different control strategy that prevents over-compensation, thereby maintaining noise cancellation effectiveness while reducing the harmful effects of excessive pressure
4Adaptability or versatility
If the acoustic environment changes dramatically, then adaptability is improved, but measurement precision of ambient noise deteriorates
Solution Approach 1:
The system uses feedback from the error microphone to continuously verify and correct the ambient noise measurement. By comparing the expected ambient noise (from the reference microphone) with the actual measured noise (from the error microphone), the system can detect and compensate for changes in acoustic environment, maintaining measurement precision even as conditions change
Solution Approach 2:
The system performs preliminary estimation of the secondary path and acoustic environment before full noise canceling operation begins. This preliminary characterization allows the system to pre-adjust its measurement and control strategies, improving the accuracy of ambient noise measurement in the upcoming environmental conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures consistent and effective noise cancellation across varying acoustic environments and ear coupling conditions, preventing undesirable anti-noise generation and improving audio intelligibility by dynamically adjusting the anti-noise signal based on ear pressure and transducer coupling.
Implementation Method 1
A reference microphone is mounted on the housing to provide a reference microphone signal indicative of the ambient audio sounds
Implementation Method 2
An error microphone is included for correcting for the electro-acoustic path from the output of the processing circuit through the transducer and to determine the degree of coupling between the user's ear and the transducer
Implementation Method 3
a transducer mounted on the housing for reproducing an audio signal that includes both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer
Implementation Method 4
an adaptive noise-canceling (ANC) processing circuit within the housing for adaptively generating an anti-noise signal from the reference microphone signal such that the anti-noise signal causes substantial cancellation of the ambient audio sounds
Data Source
AI summary
A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone is also provided proximate the speaker to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit determines a degree of coupling between the user's ear and the transducer and adjusts the adaptive cancellation of the ambient sounds to prevent erroneous and possibly disruptive generation of the anti-noise signal if the degree of coupling lies either below or above a range of normal operating ear contact pressure.