Mic Obstruction Detection in ANC Audio Devices
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Solution Overview
Problem
Personal audio devices, such as wireless telephones, face challenges in maintaining effective noise cancellation in variable acoustic environments due to the complexity and power consumption of adaptive noise canceling circuits, which can lead to undesirable results when microphones are obstructed.
Innovation Solution
Incorporating an adaptive noise-canceling (ANC) processing circuit within the device that utilizes a reference microphone and an error microphone to detect obstructions, generating an anti-noise signal to cancel ambient noise while preventing incorrect adaptation by comparing signals from these microphones, thus ensuring optimal noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive noise canceling circuits are used to improve noise cancellation in variable acoustic environments, then noise cancellation performance is improved, but device complexity and power consumption increase
Solution Approach 1:
The adaptive noise canceling circuit is divided into multiple functional modules: a reference microphone for capturing ambient noise, an adaptive filter for generating anti-noise signals, an error microphone for monitoring residual noise, and a control unit for adjusting filter coefficients. This segmentation allows each module to perform a specific function efficiently, improving overall noise cancellation performance while managing circuit complexity through modular design
Solution Approach 2:
The system implements feedback through the error microphone that continuously monitors the residual noise after anti-noise signal application. The control unit uses this feedback to dynamically adjust the adaptive filter coefficients, enabling the system to adapt to changing acoustic environments and maintain optimal noise cancellation performance without requiring overly complex fixed-structure circuits
2Reliability
If adaptive noise canceling circuits are used to adapt to environmental changes, then noise cancellation effectiveness is improved, but power consumption increases
Solution Approach 1:
The adaptive filter coefficients are updated periodically based on the error microphone feedback rather than continuously at maximum rate. The control unit adjusts the adaptation rate dynamically, increasing updates when acoustic environment changes are detected and reducing updates when the environment is stable, thereby maintaining noise cancellation effectiveness while reducing average power consumption
Solution Approach 2:
The system dynamically adjusts its operational parameters including filter adaptation rate and gain coefficients based on real-time acoustic environment assessment. This dynamic behavior allows the noise cancellation circuit to be more aggressive when needed and more conservative when the environment is stable, optimizing the trade-off between noise cancellation effectiveness and power consumption
3Adaptability or versatility
If adaptive noise canceling is implemented to handle variable acoustic environments, then adaptability is improved, but the system may generate undesirable results when microphones are obstructed
Solution Approach 1:
The control unit continuously monitors the signals from both reference and error microphones to detect potential obstructions before they cause significant degradation. When obstruction is detected (indicated by abnormal signal patterns or lack of expected acoustic correlation), the system takes preliminary action by freezing or resetting the adaptive filter coefficients to prevent incorrect adaptation that would lead to undesirable output
Solution Approach 2:
The error microphone provides critical feedback for detecting microphone obstructions. By comparing the expected error signal (based on reference microphone input and current filter coefficients) with the actual error microphone output, the system can detect when the reference microphone is obstructed (showing no correlation with actual ambient noise) or when the error microphone is obstructed (showing abnormally high residual noise), and adjust operation accordingly to maintain output quality
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 effectively adapts to changes in the acoustic environment, preventing undesirable outputs when microphones are obstructed, thereby maintaining improved intelligibility and reducing power consumption.
Implementation Method 1
a reference microphone to provide a reference microphone signal indicative of the ambient acoustic events
Implementation Method 2
an adaptive noise-canceling (ANC) processing circuit for generating an anti-noise signal from the reference microphone signal to cancel the ambient acoustic events
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
Data Source
AI summary
A personal audio device, such as a wireless telephone, includes noise canceling 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 may also be provided proximate the speaker to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit uses the reference and/or error microphone, optionally along with a microphone provided for capturing near-end speech, to determine whether one of the reference or error microphones is obstructed by comparing their received signal content and takes action to avoid generation of erroneous anti-noise.