Active Noise Cancellation Howling Suppression via Gain Enhancement
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Solution Overview
Problem
Active noise cancellation systems, particularly feedback ANC topology, face instability and tonal howling issues due to runaway amplification, leading to negative user experiences and degraded noise cancellation performance.
Innovation Solution
An audio processing system that employs a howling suppression system using a linear filter to extract howling signals, a gain enhancement subsystem to emphasize howling signals and deemphasize non-howling signals based on power ratios, and a gain control subsystem to generate a howling suppression gain signal, which is used to produce an amplified error signal and feedback signal to suppress tonal howling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback ANC topology is used to provide stable noise cancellation, then noise cancellation performance is improved, but system stability deteriorates due to runaway amplification causing tonal howling
Solution Approach 1:
The error signal processing is segmented into multiple pathways: one pathway extracts howling signals using a linear filter, another pathway processes non-howling signals, and a third pathway generates the feedback signal. This segmentation allows selective suppression of howling components while preserving stable noise cancellation functionality.
Solution Approach 2:
The howling signal is extracted and separated from the error signal using a linear filter with specific passband characteristics. By taking out the howling component, the system can apply different processing to howling and non-howling signals, preventing runaway amplification while maintaining noise cancellation performance.
2Reliability
If the feedback system amplifies the error signal to cancel external noises, then noise cancellation effectiveness is improved, but tonal howling is generated due to runaway amplification
Solution Approach 1:
The howling signal, which is a harmful byproduct of feedback amplification, is extracted and used as input for generating the howling suppression gain signal. By converting the harmful howling signal into a control input, the system suppresses runaway amplification while maintaining the beneficial noise cancellation effect.
Solution Approach 2:
The extracted howling signal is fed back through the gain enhancement subsystem to generate a suppression gain signal that modulates the feedback path. This feedback mechanism dynamically adjusts the feedback gain to prevent tonal howling while preserving noise cancellation effectiveness.
3Reliability
If conventional howling detection methods are used, then howling suppression is achieved, but false alarms occur due to inability to distinguish howling from environmental noises
Solution Approach 1:
The linear filter is designed with specific local frequency characteristics (passband and stopband) to selectively pass howling frequencies while blocking environmental noise frequencies. This local quality differentiation enables accurate distinction between howling and environmental noises, reducing false alarms.
Solution Approach 2:
The gain enhancement signal is dynamically adjusted based on the power ratio between filtered reference and error signals. This dynamic adaptation allows the system to distinguish howling from environmental noises in real-time, improving detection accuracy and reducing false alarms.
Data Source
AI summary
An audio processing system, such as an active noise cancellation system, and method suppresses tonal howling in a feedback system based on a gain enhancement system that emphasizes the howling signal and deemphasizes non-howling signals. The howling signal is extracted from an error signal generated from sound from a speaker sensed by an error sensor. The gain enhancement signal is generated based on a first power ratio between a filtered reference signal, generated based on sound sensed from external noise by a reference sensor, and a filtered error signal and/or a second power ratio between two filtered error signals with different passbands. Using the gain enhancement signal and the howling signal, a howling suppression gain signal is generated and used to amplify the error signal. A feedback signal produced based on the amplified error signal is provided to the speaker as an anti-noise signal with suppressed howling.