Echo Path Change Detector Using Power Comparison
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Solution Overview
Problem
Existing echo canceling systems in telephones face instability and divergence during abrupt changes in the echo path, particularly in speakerphones, and are prone to false positive indications of path changes, leading to echo distortion or silence.
Innovation Solution
A path change detector that compares the power of a signal output from a summation circuit to its input, using a constant multiplier and threshold comparisons, to accurately detect path changes and prevent false positives, thereby stabilizing the adaptive filter during abrupt changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a path change detector is added to detect abrupt changes in the echo path, then the system can respond to path changes, but false positive indications of path changes occur leading to divergence
Solution Approach 1:
The patent implements feedback mechanisms where the system continuously monitors the echo path and adjusts the adaptive filter coefficients based on the detected changes. The path change detector provides feedback about abrupt changes, and the system responds by adjusting the filter parameters to maintain stability while adapting to new conditions.
Solution Approach 2:
The patent employs dynamic adjustment of the adaptive filter parameters based on the detected path changes. The system transitions from a static filter configuration to a dynamic one that can adapt its coefficients in real-time when path changes are detected, allowing the system to respond to changing acoustic conditions while maintaining stability.
2Speed
If the step size in the adaptive filter algorithm is increased to improve convergence speed, then rapid adaptation is achieved, but divergence occurs during abrupt path changes
Solution Approach 1:
The patent dynamically adjusts the step size parameter of the adaptive filter based on the detected path changes. During normal operation, a larger step size is used for faster convergence, but when abrupt path changes are detected, the step size is reduced to prevent divergence and maintain stability during the transition period.
Solution Approach 2:
The patent changes the parameters of the adaptive filter algorithm based on the operational conditions. The step size and other filter parameters are adjusted according to the detected path change state, allowing the system to optimize between convergence speed and stability by switching between different parameter sets.
3Object-generated harmful factors
If echo cancellation is aggressively applied to reduce echo by 30 dB or more, then echo reduction is improved, but the desired signal may be noticeably distorted
Solution Approach 1:
The patent applies different processing characteristics to different parts of the signal processing chain. The echo cancellation is applied selectively based on the detected path change conditions, with more aggressive cancellation applied when stability is ensured and more conservative cancellation applied during transitions to prevent signal distortion.
Solution Approach 2:
The system uses feedback from the path change detector to control the aggressiveness of echo cancellation. When path changes are detected, the system adjusts the echo cancellation parameters to maintain signal integrity during the transition, preventing distortion while still achieving effective echo reduction in stable conditions.
Data Source
AI summary
A path change is detected by multiplying the energy of a signal on the output of a summation circuit in one channel of a telephone by a constant to produce a product. The product is compared with the energy of a signal on the input of the summation circuit. A path change is indicated when the energy of the product exceeds the energy of a signal on the input of the summation circuit. The comparison is made in successive frames of an audio signal and a path change is indicated when the energy of a signal on the input of the summation circuit is exceeded in two or more successive frames.