Audio Echo Cancellation Using Beam Forming and Spectral Subtraction
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Solution Overview
Problem
Existing audio systems, particularly in hands-free telecommunication devices, face challenges in effectively canceling both linear and non-linear echo components, leading to suboptimal audio quality due to the limitations of conventional echo cancellation methods which assume a linear echo path.
Innovation Solution
A device and method that separate linear and non-linear echo components using a pre-processing unit with filter units and a beam forming unit to estimate echo signals, allowing for independent control of echo cancellation through spectral subtraction, combining linear echo cancellation with beam forming to address non-linear echoes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional linear echo cancellation methods are used, then the system is simple to implement, but non-linear echo components cannot be effectively canceled leading to suboptimal audio quality
Solution Approach 1:
The echo cancellation system is segmented into multiple independent components: a pre-processing unit that estimates both linear and non-linear echo signals using separate filter units, and a post-processing unit that independently controls spectral subtraction for each echo type. This segmentation allows the system to address non-linear echoes without requiring complete redesign of the entire echo cancellation architecture.
Solution Approach 2:
The patent merges linear echo cancellation (using adaptive filters) with non-linear echo cancellation (using beam forming and spectral subtraction) into a unified system. The pre-processing unit combines outputs from both linear and non-linear echo estimation paths, allowing simultaneous cancellation of both echo types while maintaining independent control over each cancellation mechanism.
2Reliability
If high over-subtraction is used to cancel echoes, then echo suppression is improved, but speech distortion increases
Solution Approach 1:
The system applies different spectral subtraction strategies tailored to specific echo types: linear echo components are handled with standard spectral subtraction, while non-linear echo components use adapted spectral subtraction with modified parameters. This local quality approach ensures optimal echo suppression for each echo type without unnecessarily distorting speech components.
Solution Approach 2:
The patent dynamically adjusts spectral subtraction parameters based on the estimated echo signals. The post-processing unit modifies subtraction levels and frequency-dependent gains according to the characteristics of detected non-linear echoes, allowing aggressive echo suppression where needed while preserving speech quality in regions where echoes are less prominent.
3Use of energy by moving object
If linear echo cancellation only is implemented, then the system remains computationally efficient, but audio quality deteriorates due to residual non-linear echoes
Solution Approach 1:
The pre-processing unit performs preliminary estimation of non-linear echo signals using beam forming techniques before the main echo cancellation process. By pre-identifying and separating non-linear echo components from the mixed signal, the system reduces the computational burden on subsequent processing stages and enables more efficient spectral subtraction operations.
Solution Approach 2:
The patent introduces intermediate echo signal estimates as mediator variables between the raw microphone input and the final echo-cancelled output. The pre-processing unit generates intermediate representations of linear and non-linear echoes that facilitate more efficient processing in the post-processing unit, reducing overall computational complexity while improving audio quality.
Data Source
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AI summary
A method is provided which is suitable to cope with non-linear echo paths during acoustic echo cancellation in speakerphones. Non-linear paths occur particularly in hands-free operation of, e.g., a mobile phone, due to driving the amplifier and loudspeaker in the non- linear range. The idea is to combine the commonly known one microphone approach of linear acoustic echo cancellation using an adaptive filter and a post-processor together with a multiple microphone approach using beam forming which separately removes the non- linear part of the echo.