ANC Secondary Path Modeling with Sidetone Isolation
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Solution Overview
Problem
Existing wireless telephone noise canceling systems face instability and improper adaptation due to the presence of sidetone, which is not properly managed in secondary path modeling, leading to suboptimal performance in ambient noise cancellation.
Innovation Solution
A wireless telephone design that includes a reference microphone for ambient noise measurement, an error microphone for transducer output analysis, and an adaptive noise-canceling circuit that estimates the secondary path to generate an anti-noise signal, while isolating sidetone information from the adaptation process to prevent instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If sidetone is injected into the transducer output signal during a telephone conversation, then the user hears their own voice in proper relation to the telephone conversation, but the secondary path estimate becomes frustrated due to the additional path from ambient acoustic environment through the near-end speech microphone and out through the transducer, causing improper adaptation of the ANC system
Solution Approach 1:
The patent segments the signal processing paths by creating separate adaptation loops: one for the secondary path estimate that excludes sidetone, and another for the ANC adaptation that includes sidetone. This is achieved by selectively enabling/disabling sidetone injection in different signal paths and using separate adaptive filters for different adaptation purposes, thereby isolating the harmful feedback path while preserving the beneficial sidetone function
Solution Approach 2:
The patent introduces an intermediary mechanism (the selective sidetone injection controller and separate adaptation paths) that mediates between the conflicting requirements of sidetone injection and stable secondary path estimation. By controlling when and where sidetone is injected, the system allows sidetone to exist in the user output path while preventing it from contaminating the secondary path adaptation process
2Measurement precision
If the error microphone measures the transducer output to determine noise canceling effectiveness, then the ANC system can adapt the anti-noise signal, but the presence of sidetone containing ambient noise causes cancelation of side-tone and/or instability in the ANC system
Solution Approach 1:
The patent extracts the problematic sidetone component from the error microphone signal path used for secondary path adaptation. By removing sidetone injection from this specific adaptation loop while maintaining it in the user output path, the system eliminates the source of instability and improper adaptation without sacrificing the measurement precision needed for effective noise canceling
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 manages sidetone, ensuring stable and improved noise cancellation performance by isolating sidetone from the adaptation process, thereby enhancing user experience through better ambient noise reduction.
Implementation Method 1
an adaptive noise-canceling (ANC) processing circuit within the housing for adaptively generating an anti-noise signal from the reference microphone signal such that the anti-noise signal causes substantial cancellation of the ambient audio sounds
Implementation Method 2
Performance of such devices with respect to intelligibility can be improved by providing adaptive noise canceling (ANC) using a microphone to measure ambient acoustic events
Data Source
AI summary
A wireless telephone includes an adaptive noise canceling (ANC) circuit that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone is also provided proximate the speaker to provide an error signal indicative of the effectiveness of the noise cancellation. A secondary path estimating adaptive filter is used to estimate the electro-acoustical path from the noise canceling circuit through the transducer so that source audio can be removed from the error signal. Sidetone is injected into the transducer output, but is not provided to the coefficient control of the secondary path estimating adaptive filter, so that the ambient noise present in the near-end speech microphone signal, and thus present in the sidetone information, does not destabilize the ANC circuit or otherwise cause improper generation of the anti-noise signal.