Acoustic Echo Suppression via Nonlinear Distortion Modeling
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Solution Overview
Problem
Full-duplex speech communication systems face significant challenges in suppressing acoustic echoes due to nonlinear distortion caused by the non-ideal operating characteristics of loudspeaker transducers, particularly in hands-free modes of cellular phones and notebook computers, where linear echo cancellers are insufficient, allowing only up to 20 dB of echo suppression.
Innovation Solution
A speech communication apparatus incorporating a spectral shaper that divides signals into subband frequency components, uses echo cancellers and residual echo detectors to estimate and shape the acoustic echo component, and combines these to produce an echo-suppressed local signal, effectively addressing nonlinear distortion by performing calculations in the frequency domain and synchronizing timing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a linear echo canceller is used, then the device complexity is reduced, but the echo suppression capability deteriorates under severe nonlinear distortion
Solution Approach 1:
The patent segments the echo cancellation task into two distinct components: a linear echo canceller handling linear echo components and a nonlinear echo canceller handling nonlinear echo components. This segmentation allows each component to be optimized for its specific function, with the linear canceller maintaining simplicity and the nonlinear canceller providing enhanced suppression capability for distorted signals.
Solution Approach 2:
The patent creates a composite echo cancellation system that combines linear and nonlinear processing techniques. By integrating both linear adaptive filtering and nonlinear distortion compensation mechanisms, the system achieves superior echo suppression performance that neither approach could accomplish alone, particularly in hands-free telephony scenarios with severe nonlinear distortion.
2Productivity
If the loudspeaker is operated in high-powered hands-free mode, then the speech communication productivity is improved, but the nonlinear distortion of the acoustic echo path increases
Solution Approach 1:
The patent converts the harmful nonlinear distortion generated by high-powered loudspeaker operation into a可利用 characteristic by designing a nonlinear echo canceller that specifically models and cancels these distortion products. The system transforms the adverse effect of nonlinear distortion into information that can be used to improve echo suppression performance.
Solution Approach 2:
The patent changes the processing parameters by introducing nonlinear transformation functions that model the loudspeaker's distortion characteristics. By adapting the echo canceller to operate with nonlinear transfer functions and distortion models, the system maintains effective echo suppression even when operating parameters (power level, volume) cause severe nonlinear distortion.
3Device complexity
If a linear echo canceller is used with severe nonlinear distortion, then the device complexity is reduced, but the manufacturing precision of echo cancellation deteriorates
Solution Approach 1:
The patent introduces dynamic adaptation mechanisms in the nonlinear echo canceller that allow the system to automatically adjust its processing characteristics based on the current operating conditions. The nonlinear filter coefficients and distortion models are continuously adapted to match the actual loudspeaker behavior, maintaining high cancellation accuracy despite variations in operating parameters.
Solution Approach 2:
The patent implements feedback mechanisms where the output of the nonlinear echo canceller is monitored and used to continuously refine the distortion models and filter coefficients. This feedback loop enables the system to learn and adapt to the specific nonlinear characteristics of the loudspeaker, improving cancellation precision over time without increasing overall system complexity.
Data Source
AI summary
In a hands-free mode of speech communication, a loudspeaker produces acoustic energy of a distant signal from a far-end talker and a microphone produces a near-end signal containing a speech component representing the speech activity of a near-end talker or an acoustic echo component, or both. An echo replica is produced from the distant signal and a residual echo representing the difference between the near-end signal and the echo replica. The residual echo is used as a feedback signal to produce the echo replica. Using one of the near-end signal and the residual echo as a first input signal and the echo replica as a second signal, an estimate of the acoustic echo is produced when the speech activity of the near-end talker is low or zero. Using the acoustic echo estimate, the spectrum of the first input signal is shaped to produce a local signal for transmission to the far-end talker.