Adaptive Noise Cancellation Gain Control for Audio Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing feedback adaptive noise cancellation systems in personal audio devices face issues such as degradation of audio performance due to cancellation of source audio signals, variability in noise cancellation strength among users, and instability of feedback controllers, especially when the secondary path changes.
Innovation Solution
The implementation of an adaptive noise cancellation system using a combination of feedforward and feedback filters, with a programmable gain element and oversight control, that measures ambient acoustic events through reference and error microphones to generate an anti-noise signal, effectively minimizing ambient noise while maintaining audio performance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gain of the feedback controller is increased to improve noise cancellation performance, then noise cancellation strength is improved, but audio performance degrades due to cancellation of source audio signals
Solution Approach 1:
The noise cancellation system is divided into two independent paths: feedforward path that processes reference microphone signals to generate anti-noise, and feedback path that monitors error microphone signals to adjust controller gain. This segmentation allows the feedback gain to be independently controlled without affecting the source audio signal path, resolving the contradiction between noise cancellation strength and audio quality.
Solution Approach 2:
An oversight control mechanism is implemented that continuously monitors the error microphone signal and adjusts the feedback controller gain dynamically. When the error signal exceeds a threshold (indicating potential source signal cancellation), the feedback gain is reduced. This feedback loop ensures that noise cancellation performance is maintained while preventing harmful cancellation of source audio signals.
2Object-generated harmful factors
If the feedback controller gain is reduced to maintain audio performance, then audio quality is preserved, but noise cancellation performance is compromised
Solution Approach 1:
The feedback controller gain is made dynamic rather than fixed. The oversight control continuously adjusts the gain based on real-time monitoring of the error microphone signal characteristics. This allows the system to optimize noise cancellation strength for each operating condition while maintaining audio quality, resolving the trade-off between these two performance metrics.
Solution Approach 2:
The system changes the feedback controller gain parameter dynamically based on the monitored error signal characteristics. When the error signal indicates good performance, higher gain is applied for stronger noise cancellation. When the error signal suggests potential source signal interference, the gain is reduced. This parameter adaptation resolves the contradiction by optimizing both audio quality and noise cancellation strength under different conditions.
3Device complexity
If a fixed feedback controller is used to simplify the system, then device complexity is reduced, but stability deteriorates when the secondary path changes
Solution Approach 1:
The oversight control mechanism enables the feedback controller to self-adjust its gain based on real-time monitoring of system performance through the error microphone. This self-service capability allows the controller to adapt to secondary path changes (such as different user ear shapes or headphone wearing conditions) without requiring complex pre-programming or external intervention, maintaining stability while keeping the overall structure relatively simple.
Solution Approach 2:
A monitoring feedback loop is added that detects changes in system performance and adjusts the feedback controller gain accordingly. This feedback mechanism provides stability against secondary path changes by continuously optimizing the controller parameters based on actual system behavior, resolving the contradiction between simplicity and stability.
4Adaptability or versatility
If the feedback controller gain is increased to adapt to varying user conditions, then noise cancellation effectiveness is improved, but system stability may be compromised
Solution Approach 1:
The feedback controller gain is made dynamic and adaptive rather than fixed. The oversight control monitors the error microphone signal and adjusts the gain to optimize performance for each user's specific conditions (ear shape, headphone fit, etc.). This dynamic adaptation improves noise cancellation effectiveness across varying user conditions while maintaining stability through continuous monitoring and adjustment.
Solution Approach 2:
The system adapts the feedback controller gain parameter based on monitored error signal characteristics that reflect varying user conditions. By changing the gain parameter dynamically in response to user-specific acoustic paths, the system achieves both adaptability to different users and stability through controlled parameter adjustment via the oversight mechanism.
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A method for cancelling ambient audio sounds in the proximity of a transducer may include receiving an error microphone signal indicative of the output of the transducer and ambient audio sounds at the transducer. The method may also include generating an anti-noise signal for countering the effects of ambient audio sounds at an acoustic output of the transducer, wherein generating the anti-noise signal comprises applying a feedback filter having a response that generates a feedback anti-noise signal based on the error microphone signal and applying a variable gain element in series with the feedback filter. The method may further include monitoring whether an ambient audio event is occurring that could cause the feedback filter to generate an undesirable component in the anti-noise signal and controlling the gain of the variable gain element to reduce the undesirable component.