Echo Cancellation with Non-Directional Microphones
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Solution Overview
Problem
The use of directional microphones in voice communication devices is expensive and restricts design due to the need for many sound holes, making it challenging to achieve effective echo cancellation.
Innovation Solution
A voice communication system utilizing non-directional microphones with a configuration that includes a loudspeaker, two microphones, a correction unit to address amplitude differences, and an adaptive filter to cancel echo, allowing for superior echo cancellation even in small-sized devices with large distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If directional microphones are used for echo cancellation, then echo cancellation performance is improved, but cost increases and design freedom is restricted due to the need for many sound holes
Solution Approach 1:
The invention divides the microphone system into two separate microphones (first and second microphones) positioned at different locations within the housing. Each microphone captures sound from different spatial perspectives, allowing the system to separate near-end speaker voice from far-end speaker echo through signal processing rather than requiring directional microphones with multiple sound holes.
Solution Approach 2:
The invention introduces a subtraction unit that acts as an intermediary to process and combine signals from the two microphones. By subtracting the signal from the second microphone (which captures more echo) from the signal of the first microphone (which captures more near-end voice), the system achieves echo cancellation without requiring directional microphones or multiple sound holes in the housing.
2Reliability
If directional microphones are used for echo cancellation, then echo cancellation performance is improved, but cost increases
Solution Approach 1:
The invention replaces expensive directional microphones with two inexpensive non-directional microphones. While individual microphones are simpler and cheaper components, the system achieves comparable echo cancellation performance through the subtraction processing method, significantly reducing overall system cost.
Solution Approach 2:
The invention substitutes the mechanical directional sensitivity of specialized microphones with a signal processing approach. Instead of relying on the physical orientation and sound hole configuration of directional microphones, the system uses computational subtraction of microphone signals to achieve echo cancellation, replacing mechanical complexity with electronic processing.
3Volume of moving object
If the device size is reduced, then portability is improved, but echo cancellation performance deteriorates due to increased distortion in small-sized devices
Solution Approach 1:
The invention positions the two microphones at different local locations within the compact housing, with the first microphone positioned to capture near-end speaker voice with minimal echo, and the second microphone positioned to capture far-end speaker echo. This spatial differentiation allows the subtraction processing to effectively separate and cancel echo even in the constrained space of a small device.
Solution Approach 2:
The invention changes the approach from relying on physical distance and acoustic isolation (which are limited in small devices) to using signal processing parameters. By adjusting the subtraction processing to account for the specific acoustic characteristics of the compact housing, the system achieves effective echo cancellation despite the small size and associated distortion.
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 system enables superior echo cancellation in voice communication using non-directional microphones, effectively handling echo and distortion in small-sized devices with inexpensive components.
Implementation Method 1
an adaptive filter that generates an adaptive-filtered second sound pickup signal by canceling echo which varies over time, from the second sound pickup signal and a transmitted speech signal
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
A voice communication technique by which superior echo canceling can be realized even in use of non-directional microphones is provided. When voice uttered by a near end speaker is defined as speaker's voice; sound obtained by emitting a received speech signal, which is a voice signal of a far end speaker, by a loudspeaker is defined as reproduction sound; a signal obtained by picking up an acoustic signal, which contains the speaker's voice and the reproduction sound, by a first microphone is defined as a first sound pickup signal; and a signal obtained by picking up an acoustic signal, which contains the speaker's voice and the reproduction sound, by a second microphone is defined as a second sound pickup signal, a voice communication device includes: a first subtraction unit that generates a first-subtracted first sound pickup signal that is a difference between a corrected sound pickup signal and the second sound pickup signal or the first sound pickup signal, the corrected sound pickup signal being obtained by correcting either one of the first sound pickup signal and the second sound pickup signal on the basis of an amplitude difference based on a difference between a distance d1 from the loudspeaker to the first microphone and a distance d2 from the loudspeaker to the second microphone (d2 ≤ d1); and a second subtraction unit that generates a transmitted speech signal, which is to be transmitted to the far end speaker, by subtracting an adaptive-filtered second sound pickup signal, which is obtained by canceling echo, from the first-subtracted first sound pickup signal.