Acoustic Echo Cancelling System with Cavity Microphone for Non-Linear Distortion Removal
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Solution Overview
Problem
Linear echo cancellation systems are ineffective in removing non-linear distortion caused by loudspeaker transducers, leading to interference with audio signals and poor performance in hands-free kits and other mobile devices.
Innovation Solution
An audio device and method that incorporates a microphone within the loudspeaker cavity to sense non-linear distortions, using an echo canceller with adaptive filtering to subtract estimated echo components, including non-linear distortions, from the audio signal, thereby improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear echo cancellation system is used, then linear echo can be removed, but non-linear distortion from the loudspeaker cannot be removed
Solution Approach 1:
The patent segments the echo cancellation task into two separate processing stages: a linear echo canceller that removes linear echo components, and a non-linear distortion remover that eliminates non-linear distortion. This segmentation allows each component to specialize in removing specific types of interference, thereby resolving the contradiction between removing linear echo and eliminating non-linear distortion.
Solution Approach 2:
The patent introduces an intermediary component - the non-linear distortion remover - that acts as a mediator between the linear echo canceller and the output. This intermediary processes the signal further to remove non-linear distortion that the linear canceller cannot handle, thus resolving the limitation of linear systems without requiring a complete system redesign.
2Device complexity
If the microphone is placed outside the loudspeaker cavity, then the structure is simpler, but non-linear distortion cannot be sensed
Solution Approach 1:
The patent implements the nested doll principle by placing the microphone inside the loudspeaker cavity. The microphone is nested within the existing loudspeaker structure, allowing it to directly sense the acoustic environment and non-linear distortion generated by the loudspeaker without requiring external sensors or complex additional structures.
Solution Approach 2:
The loudspeaker cavity serves a dual purpose: it functions as the acoustic enclosure for the loudspeaker and simultaneously as the sensing environment for the microphone. The microphone leverages the existing acoustic field within the cavity to detect non-linear distortion, allowing the system to self-monitor without requiring separate measurement infrastructure.
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 solution effectively reduces non-linear distortion, enhancing audio signal quality and improving echo cancellation performance, particularly in compact devices where loudspeaker non-linearities are significant, by accurately accounting for and removing harmonic and intermodulation distortions.
Implementation Method 1
a microphone (124) in the loudspeaker cavity (118) to sense a signal from the loudspeaker (122)
Implementation Method 2
using an echo canceller with adaptive filtering to subtract estimated echo components
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An audio system includes a loudspeaker, a first microphone, an echo canceller, and a second microphone within the loudspeaker enclosure coupled to the loudspeaker. The first microphone provides an environmental acoustic signal to the echo canceller. The second microphone can be a high acoustic overload microphone and be placed in a back cavity of the speaker enclosure. A speaker signal is used to drive the loudspeaker, which may produce non-linear distortions in the acoustic output. The second microphone senses a signal that includes both the linear and non-linear distortions. This sensed signal is used to remove both the linear and the non-linear distortions from the environmental acoustic signal picked up from the first microphone and processed by the echo canceller.