Inter-channel coherence reduction for acoustic echo cancellation
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Solution Overview
Problem
Stereophonic and multichannel acoustic echo cancellation systems face challenges due to non-uniqueness and ill-conditioned equations, leading to performance issues when there are acoustic changes in the transmission room, and existing methods struggle to effectively decorrelate inter-channel cross-correlation without causing distortion, especially at lower frequencies.
Innovation Solution
The introduction of an inter-channel amplitude coherence reduction method using amplitude modulation in conjunction with phase modulation, specifically tailored for the low-frequency range, to enhance the effectiveness of acoustic echo cancellation, ensuring decorrelation without noticeable distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase modulation is used to decorrelate inter-channel cross-correlation, then decorrelation effectiveness is improved, but distortion is introduced at lower frequencies
Solution Approach 1:
The patent applies amplitude modulation as an alternative parameter change to decorrelate the stereo channels. Instead of modifying phase parameters which cause distortion at low frequencies, the invention modulates the amplitude of each channel with different modulation signals, achieving decorrelation while preserving the original phase information and avoiding audible distortion.
2Reliability
If amplitude modulation is applied to reduce inter-channel coherence at low frequencies, then decorrelation is achieved without distortion, but system complexity increases
Solution Approach 1:
The patent replaces complex mechanical or acoustic decorrelation methods with electronic amplitude modulation. By using simple amplitude modulation signals applied to each channel, the invention achieves the desired decorrelation effect without requiring complex physical systems or signal processing architectures.
3Reliability
If inter-channel decorrelation is increased to stabilize echo cancellation, then convergence reliability is improved, but spatial image accuracy deteriorates
Solution Approach 1:
The patent employs dynamic amplitude modulation where the modulation depth and frequency can be adjusted based on the acoustic environment and signal characteristics. This dynamic approach allows the system to achieve sufficient decorrelation for stable echo cancellation convergence while maintaining the spatial image accuracy by adapting the modulation parameters to preserve perceptually important signal features.
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
This approach effectively reduces coherence between transmission channels, stabilizing the echo cancellation process and preserving the original spatial image, even at low frequencies, while minimizing perceivable spectral distortion.
Implementation Method 1
an inter-channel amplitude coherence reduction method using amplitude modulation in conjunction with phase modulation
Implementation Method 2
using amplitude modulation in conjunction with phase modulation, specifically tailored for the low-frequency range
Data Source
AI summary
In an audio system having acoustic echo, incoming audio signals are decorrelated by applying both phase modulation and amplitude modulation. The resulting decorrelated signals are rendered by loudspeakers, and co-located microphones generate outgoing audio signals that include echo signals caused by the existence of acoustic echo paths from the loudspeakers to the microphones. Acoustic echo cancellation (AEC) is applied to the outgoing audio signals to reduce the amount of echo in those signals. Decorrelating the incoming audios signals using amplitude modulation in addition to phase modulation can increase the effectiveness of the AEC processing. In a frequency-domain implementation, the amount of amplitude modulation can be different for different frequency bands (e.g., greater amplitude modulation for lower frequencies corresponding to human speech and/or no amplitude modulation for higher frequencies).