Echo Path Change Counter for Echo Cancellers
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Solution Overview
Problem
Existing echo cancellers face difficulty in distinguishing between echo path changes and double talk conditions, leading to poor echo removal and intrusive echo perception when network delays exceed 36 ms, as they often confuse new hybrid echoes with converged adaptive filter echoes.
Innovation Solution
A method using an Echo Path Change Counter that monitors Echo Return Loss (ERL), Echo Return Loss Enhancement (ERLE), noise levels, and signal energies to differentiate between echo path changes and double talk scenarios, incrementing or decrementing the counter based on specific thresholds to determine probable new line conditions and facilitate re-convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the echo canceller uses adaptive filtering to cancel echo, then echo removal effectiveness is improved, but the ability to distinguish between echo path changes and double talk conditions deteriorates
Solution Approach 1:
The invention segments the echo cancellation system into multiple independent components: an adaptive filter for echo cancellation, a double talk detector for detecting double talk conditions, and an echo path change detector for detecting echo path changes. Each component operates independently with its own detection logic, allowing the system to maintain high echo removal effectiveness while accurately distinguishing between different conditions.
Solution Approach 2:
The invention introduces an intermediary echo path change detector that acts as a mediator between the adaptive filter and the double talk detector. This intermediary component analyzes the echo return loss enhancement (ERLE) and other parameters to determine whether echo path changes have occurred, preventing the adaptive filter from incorrectly adapting to double talk conditions while maintaining its echo cancellation capability.
2Object-affected harmful factors
If the echo canceller quickly re-converges to new echo path, then echo perception is reduced, but the complexity of detecting and responding to line changes increases
Solution Approach 1:
The invention performs preliminary detection of echo path changes by monitoring parameters such as echo return loss enhancement (ERLE) and double talk detector output before the adaptive filter can be misled by double talk conditions. When an echo path change is detected, the system proactively resets or adjusts the adaptive filter coefficients, preventing echo perception rather than reacting after the problem occurs.
Solution Approach 2:
The invention implements a feedback mechanism where the echo path change detector continuously monitors the echo return loss enhancement (ERLE) and other system parameters, and feeds this information back to control the adaptive filter's convergence behavior. This feedback loop enables the system to automatically detect and respond to echo path changes, maintaining low echo perception without requiring complex manual intervention.
3Object-generated harmful factors
If the hybrid provides good signal matching, then echo reflection is reduced, but the cost and cabling requirements for four-wire circuits increase
Solution Approach 1:
The invention replaces the mechanical/electrical solution of improving hybrid matching (which would require better four-wire circuit implementation and more expensive equipment) with a signal processing solution. The adaptive filter and echo path change detection system digitally cancel echo reflections, achieving the same effect as perfect hybrid matching without requiring complex four-wire circuitry or expensive hardware modifications.
Data Source
AI summary
A method for detecting echo path changes in an echo canceller using the statistics of the echo canceling behavior (i.e. signal and performance information), to distinguish between new line and double talk conditions. A moving counter is incremented or decremented based on monitored levels of ERL (Echo Return Loss), ERLE (Echo Return Loss Enhancement), noise and signal energies. When the counter reaches a predetermined threshold value indicative of sustained poor echo cancellation performance, a determination is made that there is a probable new line condition (i.e. echo path change). This echo path change information is then passed to the echo canceller to enable re-convergence.