Acoustic Echo Cancellation Using Enclosure Microphone Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional acoustic echo cancellation techniques fail to effectively remove nonlinear components of echo signals without distorting the desired speech, especially in small loudspeakers used in devices like smartphones, which result in significant nonlinear echo components and speech distortion when driven loudly.
Innovation Solution
A system that uses a microphone inside the loudspeaker enclosure to generate an improved acoustic echo cancellation reference signal by combining low-frequency and high-frequency signals, derived through optimal transfer functions and filtering, to estimate loudspeaker displacement and force factor, effectively canceling echo while preserving speech quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AEC techniques are used to remove nonlinear components of echo, then echo cancellation performance is improved, but speech distortion increases
Solution Approach 1:
The patent segments the echo signal into linear and nonlinear components, and further divides the nonlinear components into different frequency ranges (low-frequency below 1kHz and high-frequency above 1kHz). Different cancellation strategies are applied to each segment: linear echo is cancelled using conventional AEC, low-frequency nonlinear echo is cancelled using a low-pass filtered reference signal, and high-frequency nonlinear echo is cancelled using a high-pass filtered reference signal. This segmentation allows selective cancellation without affecting speech quality.
Solution Approach 2:
The patent applies different quality characteristics to different frequency components of the echo signal. Low-frequency nonlinear components are handled with a low-pass filtered reference signal that preserves speech components, while high-frequency nonlinear components are handled with a high-pass filtered reference signal that removes speech components. This local differentiation allows effective cancellation of nonlinear echo components while preserving speech integrity in each frequency band.
2Power
If small loudspeakers are driven loudly to improve audio output, then sound pressure level is improved, but nonlinear echo components increase
Solution Approach 1:
The patent uses feedback by capturing the loudspeaker output with a microphone and using this captured signal as a reference for echo cancellation. The reference signal is processed through low-pass and high-pass filters to create frequency-specific cancellation signals that are subtracted from the microphone input. This feedback mechanism allows the system to adaptively cancel nonlinear echo components generated at high power levels without requiring changes to the loudspeaker operation.
3Reliability
If frequency-based signal separation is applied to cancel nonlinear echo, then echo cancellation performance is improved, but system complexity increases
Solution Approach 1:
The patent implements dynamic signal processing by applying frequency-dependent filtering and cancellation strategies. The system dynamically selects different processing paths based on frequency content: low-pass filtering for low-frequency nonlinear components and high-pass filtering for high-frequency nonlinear components. This dynamic approach allows effective echo cancellation across different frequency ranges while maintaining computational efficiency through straightforward filter implementations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The improved reference signal achieves at least a 6.4 dB better echo cancellation performance compared to standard methods, effectively reducing echo while minimizing speech distortion, especially when loudspeakers are driven loudly.
Implementation Method 1
a microphone inside the loudspeaker enclosure provides a signal used to generate an acoustic echo cancellation reference signal
Data Source
AI summary
Systems and methods for improved acoustic echo cancellation are provided. In various embodiments, a microphone located in the loudspeaker enclosure provides a first signal that is used to estimate the loudspeaker displacement which is proportional to the sound pressure level (SPL) inside the enclosure. A second signal is then derived by mapping the displacement to the loudspeaker's force factor (Bl(x)) and then modulating this by a measured current to a voice coil inside the speaker to provide an estimate of the force acting on the moving mass of the loudspeaker. The first signal is highly correlated with the echo signal for low frequencies and the second signal is highly correlated with the echo signal for high frequencies. The two signals are then combined to provide a single improved AEC reference signal.