Stereo Echo Cancellation Using Adaptive Filter Segmentation
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Solution Overview
Problem
Existing two-way communications systems, particularly those using stereo speakers, face challenges in effectively canceling echoes due to increased distortion and computational complexity when attempting to isolate and remove sound waves picked up by microphones, especially in VoIP applications.
Innovation Solution
The method involves subtracting far-end signals to generate difference signals, approximating echoes using adaptive filters with varying adaptation rates based on signal strengths or correlation, and optionally subdividing signals into sub-bands for processing, including non-linear techniques to enhance echo cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If speaker signals are conditioned to be orthogonal to isolate and cancel echo, then echo cancellation effectiveness is improved, but distortion increases and computational complexity increases significantly
Solution Approach 1:
The patent divides the stereo signal processing into separate mono channel processing paths. Each adaptive filter processes individual mono signals independently, avoiding the need for complex orthogonal conditioning of stereo signals. This segmentation reduces computational complexity while maintaining echo cancellation effectiveness through independent adaptation of each channel's filter coefficients.
Solution Approach 2:
The patent changes the approach from orthogonal signal conditioning to using adaptive filter parameters that automatically adjust to optimal values. The adaptive filters modify their impulse responses based on minimizing echo in the captured signal, eliminating the need for complex pre-conditioning while achieving effective echo cancellation through parameter adaptation.
2Reliability
If speaker signals are conditioned to be orthogonal to isolate and cancel echo, then echo cancellation effectiveness is improved, but signal distortion increases
Solution Approach 1:
The adaptive filters perform self-adjustment by automatically modifying their coefficients based on the actual acoustic environment and signal characteristics. This self-service mechanism eliminates the need for external orthogonal conditioning that would distort signals, as the filters naturally adapt to cancel echo while preserving the original signal content through autonomous coefficient optimization.
Solution Approach 2:
The system uses feedback from the microphone signal to continuously adjust adaptive filter coefficients. The filtered output is fed back to update the filter parameters, creating a closed-loop system that cancels echo effectively without introducing distortion. This feedback mechanism allows the system to adapt to changing acoustic conditions while maintaining signal fidelity.
Data Source
AI summary
Acoustic echoes in communications systems are distracting and undesirable. Acoustic echoes occur in communications systems where sound produced by a speaker is picked up by a microphone in a communications system. In a stereo playback environment, echo cancellation techniques become more complicated. Echo cancellation can be performed by performing echo cancellation on a center signal, which is the sum of a left channel signal and the right channel signal, or left signal and a difference signal, which is the difference of the right channel signal and the left channel signal. The adaptation rates of the two echo cancellers meet certain constraints to prevent degeneracies in the echo cancellation system.