Dual Adaptive Filter Acoustic Echo Cancellation
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Solution Overview
Problem
Existing full-duplex hands-free audio communication systems face significant challenges in controlling howling due to high positive gains in electro-acoustic loops over wide frequency ranges, as previous methods often rely on howling detection, adaptive notch filters, or frequency shifting, which can compromise speech quality or fail to detect howling effectively.
Innovation Solution
An acoustic echo canceller with a dual adaptive filter structure, where a shorter transversal adaptive echo cancellation filter adapts during periods of silence to track changes in the echo path and suppress howling, selecting the lower power error signal for transmission, thereby avoiding the need for howling detection and maintaining full-duplex capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long adaptive filter is used for acoustic echo cancellation, then echo cancellation performance is improved, but computational complexity and adaptation time increase
Solution Approach 1:
The patent divides the echo cancellation task into two separate adaptive filters: a long filter for general echo cancellation and a short filter for howling suppression. This segmentation allows each filter to be optimized for its specific function, with the short filter requiring fewer computations while the long filter handles the broader echo cancellation task.
Solution Approach 2:
The short adaptive filter is designed to provide partial echo cancellation focused specifically on suppressing howling frequencies. Rather than attempting to cancel all echo components, the short filter concentrates computational resources on the critical howling suppression function, achieving effective results with reduced complexity.
2Object-affected harmful factors
If switched loss is applied to control howling, then howling suppression is improved, but speech quality deteriorates due to significant half-duplex behavior
Solution Approach 1:
The patent replaces the mechanical switched loss approach with an adaptive filtering system. Instead of abruptly switching between full-duplex and half-duplex modes, the adaptive filters continuously adjust their coefficients to suppress howling while maintaining smooth full-duplex operation, thereby preserving speech quality without the harsh transitions characteristic of switched loss methods.
3Object-affected harmful factors
If adaptive notch filters are used for howling control, then howling suppression is improved, but speech quality is compromised due to frequency shifting effects
Solution Approach 1:
The patent changes the approach from frequency-domain notch filtering to time-domain adaptive filtering. The adaptive filters operate in the time domain, adapting their impulse response to match the echo path characteristics, which avoids the frequency shifting and spectral distortion issues inherent in adaptive notch filter approaches.
4Device complexity
If a short adaptive filter is used for anti-howling, then computational complexity is reduced, but echo cancellation performance may be insufficient
Solution Approach 1:
The patent merges the functions of the long and short adaptive filters through a combined output structure. The outputs of both filters are summed together, allowing the short filter to contribute specialized howling suppression while the long filter provides comprehensive echo cancellation. This merging ensures that neither filter's limitations are problematic, as they complement each other's strengths.
Data Source
Figure 1~2
Figure 3
AI summary
A howling control structure for a full duplex communication system. The structure is implemented as part of an acoustic echo canceller having a conventional transversal adaptive filter. A second transversal adaptive filter, shorter than the conventional filter, that adapts even in the absence of speech in its reference signal, is provided. The short filter adapts quickly and provides enough echo cancellation to prevent howling from occurring, even if the echo path is changed significantly during silence periods.