Acoustic Echo Cancellation Using Internal Pressure-Gradient Microphone
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Solution Overview
Problem
Conventional audio devices struggle to effectively filter both linear and non-linear components of echo from near-end signals due to non-linear distortions introduced by loudspeaker transducers, which can lead to residual echo suppression causing further distortion in the near-end signal.
Innovation Solution
An audio system with a pressure-gradient microphone positioned in the rear acoustic chamber of the loudspeaker transducer to detect radiated output, providing a reference signal that is used to filter the near-end signal, along with a processor to determine the diaphragm velocity and generate a clean near-end signal by combining reference signals from different frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional AEC filters the estimated far-end signal from the observed near-end signal, then linear echo components are removed, but non-linear components remain causing residual echo
Solution Approach 1:
The patent segments the echo cancellation process into two distinct stages: first filtering linear components using conventional AEC with the far-end reference signal, then separately filtering non-linear components using an internal microphone that captures only the loudspeaker's radiated sound. This segmentation allows each filter to specialize in removing specific types of echo components without interfering with the other.
Solution Approach 2:
The internal microphone acts as an intermediary device that directly measures the loudspeaker's radiated output within the enclosure. This intermediary measurement provides a clean reference signal that contains only the non-linear distortion components introduced by the loudspeaker, which can then be used to selectively remove these components from the near-end signal without affecting linear components already handled by conventional AEC.
2Measurement precision
If residual echo suppression is applied to remove non-linear components, then echo reduction is improved, but further distortion is introduced into the near-end signal
Solution Approach 1:
The patent converts the harmful non-linear distortion components into a useful reference signal by using the internal microphone to capture them directly at the source. Instead of attempting to suppress these components after they have mixed with the near-end signal (which causes distortion), the system uses the internally captured non-linear components as a clean reference for selective filtering, thereby eliminating the need for aggressive suppression that would distort the near-end signal.
3Measurement precision
If an internal microphone is positioned in the rear acoustic chamber to detect loudspeaker output, then non-linear echo components are captured, but device complexity increases
Solution Approach 1:
The internal microphone positioned in the rear acoustic chamber serves multiple functions simultaneously: it captures the loudspeaker's radiated sound for non-linear echo cancellation, and can also be used for acoustic echo path identification and system diagnostics. This multi-functionality justifies the additional component by providing multiple benefits from a single addition rather than requiring separate devices for each function.
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
This approach significantly reduces echo, including non-linear components, by accurately representing the loudspeaker's radiated sound, resulting in a cleaner near-end signal with less distortion compared to conventional echo cancellation methods.
Implementation Method 1
a pressure-gradient microphone positioned in a rear acoustic chamber of the loudspeaker transducer to detect a radiated output from the loudspeaker transducer
Data Source
AI summary
An audio system includes an external microphone to receive a near-end audio content and a loudspeaker transducer and a corresponding enclosure defining an acoustic chamber. An internal pressure-gradient microphone is positioned in the acoustic chamber to detect a radiated output from the loudspeaker transducer. The audio system also includes a processor and a memory having instructions that, when executed by the processor, cause the audio system to receive a near-end signal from the external microphone and a reference signal from the internal microphone. The instructions, when executed, further cause the processor to cause the audio system to filter the reference signal from the near-end signal to define a clean near-end signal, and to emit the clean near-end signal. Related principles are described by way of reference to method and apparatus examples.