Stereo Echo Suppression via Correlation Removal

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Solution Overview

Problem

Existing stereo echo cancellers face coefficient indeterminacy issues when dealing with correlated signals between the Left and Right channels, leading to excessive suppression and deterioration in sound quality.

Innovation Solution

A stereo echo suppressing device that operates in the frequency domain, calculating amplitude spectra for both channels and estimating echo signals using stored echo path characteristics, while rejecting correlation components to prevent excessive suppression.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an adaptable algorithm is used in a stereo echo canceller to suppress acoustic echo signals, then echo suppression performance is improved, but coefficient indeterminacy occurs when there is correlation between Left and Right channels of far-end signals

Engineering Contradiction:

Improveecho suppression performanceVSAvoidecho path characteristic estimation accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent extracts and removes the correlated component from the far-end signals before processing. By separating the correlated portion that causes coefficient indeterminacy from the independent signal components, the system can apply adaptive algorithms without suffering from the correlation problem, thus resolving the contradiction between echo suppression performance and estimation accuracy

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces asymmetric processing for the Left and Right channels by selectively applying different operations based on correlation detection. When correlation is detected, asymmetric handling is applied to break the symmetry that causes coefficient indeterminacy, allowing the adaptive algorithm to converge properly while maintaining echo suppression effectiveness

Inventive Principle:

Principle #4Asymmetry

2Measurement precision

If non-correlated noises and cross-correlation variations are added to far-end signals to solve coefficient indeterminacy, then coefficient indeterminacy problem is resolved, but far-end signals are distorted and sound quality deteriorates

Engineering Contradiction:

Improveecho path characteristic estimation accuracyVSAvoidsignal distortion

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

Instead of adding artificial noise to break correlation (which causes distortion), the patent converts the harmful correlated signal into a beneficial component by explicitly estimating and removing it. This approach resolves coefficient indeterminacy without introducing signal distortion, as the correlated component is naturally present in the signal rather than being artificially added

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If echo suppression is performed in frequency domain without adaptable algorithm, then coefficient indeterminacy problem is avoided, but too much suppression occurs when correlated signals are inputted

Engineering Contradiction:

Improveecho path characteristic estimation accuracyVSAvoidecho suppression performance

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent segments the echo suppression process into distinct stages: first removing correlated components from far-end signals, then performing frequency-domain echo suppression on the decorrelated signals. This segmentation allows each stage to optimize for its specific function, preventing over-suppression while maintaining estimation accuracy

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs preliminary decorrelation processing on the far-end signals before applying echo suppression. By pre-removing correlated components, the subsequent echo suppression operates on already-processed signals, preventing too much suppression from occurring while maintaining reliable echo cancellation performance

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9531884B2Stereo echo suppressing device, echo suppressing device, stereo echo suppressing method, and non-transitory computer-readable recording medium storing stereo echo suppressing program

Publication Date: 2016.12.27 OKI ELECTRIC INDUSTRY CO LTD

AI summary

According to the embodiment of the present invention, the stereo echo suppressing device that suppresses an acoustic echo signal based on a near-end input signal and far-end signals of two channels as a stereo signal includes: first and second far-end signal amplitude spectrum calculating units for calculating amplitude spectrums of a first far-end signal and a second far-end signal; a near-end input signal amplitude spectrum calculating unit for calculating an amplitude spectrum of the near-end input signal; first and second estimation echo signal estimating units for estimating amplitude spectrums of a first estimation echo signal and a second estimation echo signal; first and second echo suppressing units for suppressing the acoustic echo signal; first and second echo path characteristic updating unit for calculating and updating echo path characteristics of the first far-end signal and the second far-end signal.