Biquad Filter Coefficient Adjustment for ANC Audio Quality
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing feedback adaptive noise cancellation systems in personal audio devices face challenges such as degrading audio performance due to noise cancellation of source audio signals, varying noise cancellation strength across users, and adverse effects in low-ambient noise environments, particularly impacting signal magnitude and phase relationships.
Innovation Solution
An integrated circuit with a processing circuit that includes a feedback path comprising a plurality of biquad filters and an event detection and oversight control system, which generates an anti-noise signal by monitoring ambient audio events and adjusts filter coefficients to reduce undesirable components, thereby improving noise cancellation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback adaptive noise cancellation is used to cancel ambient noise, then noise cancellation performance is improved, but source audio signals are degraded due to cancellation of portions of the source audio signal
Solution Approach 1:
The feedback filter is segmented into multiple biquad filters, each handling specific frequency ranges. This segmentation allows selective adjustment of filter coefficients for different frequency components, enabling the system to cancel noise in certain frequencies while preserving source audio signals in other frequencies, thus resolving the contradiction between noise cancellation performance and source audio quality
Solution Approach 2:
The system dynamically changes filter coefficients of the biquad filters based on detected ambient audio events and low-ambient conditions. By adjusting parameters such as feedback gain and filter coefficients adaptively, the system optimizes noise cancellation effectiveness while minimizing degradation of source audio signals across different operating conditions
2Object-affected harmful factors
If feedback gain is strongly attenuated to reduce signal boosting at particular frequencies, then system noise is reduced, but adaptive noise cancellation at other frequencies is reduced
Solution Approach 1:
Different biquad filters are applied to different frequency ranges with locally optimized coefficients. This allows the system to reduce system noise at specific frequencies where signal boosting occurs while maintaining strong adaptive noise cancellation at other frequencies, resolving the contradiction between reducing system noise and preserving noise cancellation effectiveness
Solution Approach 2:
The feedback gain and filter coefficients are made dynamic rather than fixed. The system continuously adapts the filter parameters based on real-time analysis of ambient audio events and low-ambient conditions, enabling optimal noise cancellation performance across varying frequency spectra while minimizing unwanted signal boosting
3Device complexity
If fixed feedback controller is used for simplicity and low cost, then device complexity is reduced, but noise cancellation strength varies significantly across different users
Solution Approach 1:
The feedback controller transitions from a fixed design to a dynamic adaptive system. The biquad filter coefficients are automatically adjusted based on individual user characteristics and ambient conditions detected by the error microphone, enabling the system to adapt to different users without increasing physical device complexity
Solution Approach 2:
The error microphone provides feedback about the actual acoustic environment and noise cancellation effectiveness. This feedback is used to continuously adjust the biquad filter coefficients, enabling the system to adapt to individual user variations in ear shape, headphone fit, and ambient conditions while maintaining a relatively simple device architecture
Data Source
AI summary
An integrated circuit may include an output for providing an output signal to a transducer including both a source audio signal for playback to a listener and an anti-noise signal for countering the effect of ambient audio sounds in an acoustic output of the transducer, an error microphone input for receiving an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer, and a processing circuit. The processing circuit may implement a feedback path comprising a feedback filter having a response that generates a feedback anti-noise signal based on the error microphone signal, the feedback filter comprising a plurality of biquad filters and wherein the anti-noise signal is generated from the feedback anti-noise signal and an event detection and oversight control that detects that an ambient audio event is occurring that could cause the feedback filter to generate an undesirable component in the anti-noise signal, and controls filter coefficients of one or more of the plurality of biquad filters to reduce the undesirable component.