Echo Cancellation With Adaptive Bulk Delay Control
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Solution Overview
Problem
Modern voice conference bridge architectures using IP packet-based methods face issues with line echo due to discontinuities in the transmission path, which can lead to voice quality degradation, especially when network jitter causes adaptive jitter buffers to introduce time-varying delays that destabilize echo cancellers.
Innovation Solution
An adaptive bulk delay control mechanism is introduced to synchronize the bulk delay in the echo canceller's signal path with the adaptive jitter buffer's delay, maintaining time-invariance and preventing echo canceller divergence by continuously adjusting the bulk delay to match the current jitter buffer length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive jitter buffer is used to accommodate variable network jitter, then voice quality is improved by avoiding data starvation, but echo canceller stability deteriorates due to time-varying delays
Solution Approach 1:
The system implements feedback by having the jitter buffer communicate its current delay state to the echo canceller, which then adjusts the bulk delay accordingly. This closed-loop feedback mechanism allows the echo canceller to compensate for the time-varying delays introduced by the adaptive jitter buffer, maintaining stability while preserving voice quality improvements.
Solution Approach 2:
The invention changes the parameter of bulk delay in the echo canceller to dynamically match the jitter buffer's delay characteristics. By adjusting the bulk delay parameter in response to jitter buffer state changes, the system maintains time-invariance in the overall signal path, resolving the stability issue while keeping the adaptive jitter buffer active for voice quality improvement.
2Stability of the object's composition
If fixed jitter buffer depth is used to accommodate worst case network jitter, then echo canceller stability is maintained, but voice quality deteriorates when network jitter exceeds buffer depth causing data starvation
Solution Approach 1:
The system transitions from a static fixed buffer depth to a dynamic adaptive buffer depth that responds to actual network conditions. The jitter buffer automatically adjusts its depth based on current jitter levels, allowing it to accommodate varying network conditions without compromising either echo canceller stability or voice quality, thereby resolving the contradiction between stability and reliability.
Solution Approach 2:
The feedback mechanism allows the jitter buffer to monitor its own delay characteristics and communicate this information to the echo canceller. This enables the system to adapt the bulk delay dynamically, ensuring that the echo canceller remains stable while the jitter buffer can expand its depth when needed to prevent data starvation and maintain voice quality.
3Reliability
If jitter buffer depth is increased to accommodate larger delays, then data starvation is prevented, but echo tail delay becomes more variable causing echo canceller divergence
Solution Approach 1:
The invention changes the bulk delay parameter in the echo canceller to dynamically match the jitter buffer's delay characteristics. By adjusting the bulk delay parameter in response to jitter buffer state changes, the system maintains time-invariance in the overall signal path, resolving the stability issue while keeping the adaptive jitter buffer active for voice quality improvements.
Solution Approach 2:
The system implements feedback by having the jitter buffer communicate its current delay state to the echo canceller, which then adjusts the bulk delay accordingly. This closed-loop feedback mechanism allows the echo canceller to compensate for the time-varying delays introduced by the adaptive jitter buffer, maintaining stability while preserving voice quality improvements.
Data Source
AI summary
In an example embodiment, a control connection is introduced between an adaptive jitter buffer (AJB) and an adaptive bulk delay (ABD) buffer of an echo canceller (ECAN) in an Internet Protocol (IP) conference bridge. The control connection allows the AJB to control the amount of delay inserted by the ABD in the ECAN convolution processor (CP) signal path. The adjustment in ABD delay restores the time alignment of the ECAN internal echo estimate and offsets variations in echo tail delay introduced by network induced AJB delay changes. Time-invariance is preserved in the echo tail path.