Partitioned ANC Filter Architecture for Stable Noise Cancellation
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Solution Overview
Problem
Personal audio devices, such as wireless telephones, face challenges in maintaining effective noise cancellation under dynamically changing operating conditions, leading to disruptions in ambient noise cancellation due to events like nearby voice activity or wind, which require resetting the adaptive filter, resulting in temporary loss of noise-canceling performance.
Innovation Solution
The implementation of a partitioned adaptive filter architecture with a fixed and variable frequency response portion, combined with an error microphone for controlling the adaptation of the anti-noise signal, allows for immediate noise cancellation during filter reset and increased stability by minimizing deviation from a nominal response, using leakage to restore the filter response over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the adaptive filter is reset in response to disruptive events (voice activity, wind, mechanical noise), then the stability and reliability of noise cancellation is improved under changing conditions, but the noise cancellation performance is lost temporarily while the filter re-adapts
Solution Approach 1:
The adaptive filter is segmented into a fixed filter portion and a variable filter portion. The fixed portion maintains a nominal frequency response that provides baseline noise cancellation, while the variable portion adapts to changing conditions. During reset events, the fixed portion ensures continuous noise cancellation while the variable portion re-adapts, eliminating the gap where no cancellation occurs.
Solution Approach 2:
The fixed filter portion is pre-configured with a nominal frequency response that provides adequate noise cancellation for typical conditions. This preliminary setup ensures that when reset events occur, noise cancellation is already active and continuous, rather than starting from zero during re-adaptation.
2Adaptability or versatility
If a traditional adaptive filter is used that fully adapts to environmental changes, then the adaptability to different acoustic conditions is improved, but the system becomes unstable under dynamically changing conditions requiring frequent resets
Solution Approach 1:
By dividing the adaptive filter into fixed and variable portions, the system achieves a balance between adaptability and stability. The variable portion provides adaptability to changing acoustic conditions, while the fixed portion maintains stability by preserving the nominal frequency response. This segmentation allows the system to adapt without fully committing to potentially unstable adaptations.
Solution Approach 2:
Different portions of the filter have different qualities: the fixed portion maintains a stable nominal response suitable for typical conditions, while the variable portion provides adaptive response for changing conditions. This local differentiation allows each portion to optimize for its specific function, achieving both stability and adaptability simultaneously.
Data Source
AI summary
A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cancel ambient audio sounds. A processing circuit implements one or more adaptive filters that control the generation of the anti-noise signal. At least one of the adaptive filters is partitioned into a first portion having a fixed frequency response and a second portion having a variable frequency response. The partitioned filter may be an adaptive filter that generates the anti-noise signal directly from the reference microphone signal. An error microphone may be provided to measure the ambient sounds and transducer output near the transducer, and a secondary path adaptive filter included to generate an error signal from the error microphone signal, which may be partitioned, alone or in combination.