Adaptive Noise-Canceling Filter Path Estimation Control
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Solution Overview
Problem
Existing personal audio devices, such as wireless telephones, face challenges in accurately updating secondary and leakage path estimates for noise cancellation when source audio is absent or low in amplitude, leading to suboptimal noise-canceling performance.
Innovation Solution
Incorporating an adaptive noise-canceling (ANC) circuit that measures ambient acoustic environments and generates anti-noise signals, with a secondary path estimating adaptive filter to remove source audio from error microphone signals and a leakage path estimating adaptive filter to correct reference microphone signals, while only adapting these estimates when sufficient source audio magnitude relative to ambient sounds is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the secondary path estimate and leakage path estimate are continuously updated using error microphone signal and reference microphone signal, then the noise-canceling performance should be improved, but when source audio is absent or low in amplitude, the estimates cannot be accurately updated as the signals are dominated by other sounds
Solution Approach 1:
The patent changes the operational parameters of the adaptive filter by introducing a control mechanism that adjusts whether adaptation occurs based on the presence and amplitude of source audio. When source audio is detected above a threshold, the secondary path and leakage path estimates are updated; when source audio is absent or below threshold, updates are prevented. This parameter-based control resolves the contradiction by adapting the estimation process to the current acoustic conditions.
2Adaptability or versatility
If the adaptive filter is allowed to adapt continuously, then the noise-canceling should respond to changing environments, but the secondary path estimate and leakage path estimate may not be accurately updated when source audio is low in amplitude
Solution Approach 1:
The patent implements a feedback mechanism where the adaptive filter's adaptation process is monitored and controlled based on the detected source audio levels. The system continuously monitors the error microphone signal and reference microphone signal to determine whether source audio is present, and uses this feedback to enable or disable the adaptation of path estimates. This feedback loop ensures that updates only occur when reliable data is available, maintaining both adaptability and reliability.
3Productivity
If the error microphone signal and reference microphone signal are used for updating path estimates, then the noise-canceling performance should be optimized, but when source audio is absent, these signals are dominated by other sounds making accurate updates impossible
Solution Approach 1:
The patent applies preliminary action by checking for the presence of source audio before attempting to update the path estimates. The system performs a preliminary detection of source audio amplitude and presence in the error and reference signals, and only proceeds with the adaptation process when the preliminary check confirms sufficient source audio is present. This prevents loss of information by avoiding updates when the signals are dominated by other sounds.
Data Source
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AI summary
A personal audio device, such as a wireless telephone, generates an anti-noise signal from a microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. The microphone measures the ambient environment, but also contains a component due to the transducer acoustic output. An adaptive filter is used to estimate the electro-acoustical path from the noise-canceling circuit through the transducer to the at least one microphone so that source audio can be removed from the microphone signal. A determination of the relative amount of the ambient sounds present in the microphone signal versus the amount of the transducer output of the source audio present in the microphone signal is made to determine whether to update the adaptive response.