Active Noise Cancelling Feedback Gain Control
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Solution Overview
Problem
Active noise canceling systems in headphones face reduced performance due to the need for stability in all configurations, leading to suboptimal noise cancellation as the canceling filter is designed based on worst-case assumptions for varying secondary path transfer functions, resulting in increased complexity and reduced effectiveness.
Innovation Solution
The system adjusts the gain of the feedback loop based on measured secondary path variations, maintaining constant frequency and phase response of the canceling filter, allowing for improved noise cancellation without altering the transfer function, thereby reducing stability constraints and enhancing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the canceling filter is designed based on worst-case assumptions for the secondary path transfer function to ensure stability in all configurations, then system stability is improved, but noise cancellation performance deteriorates
Solution Approach 1:
The patent applies dynamics by making the feedback gain adjustable based on the operational configuration. Instead of using a fixed worst-case gain, the system dynamically adapts the feedback gain according to the actual secondary path transfer function characteristics. This allows the system to maintain stability while optimizing noise cancellation performance for each specific configuration, resolving the contradiction between over-designed stability and actual performance.
2Manufacturing precision
If the canceling filter is made adaptive to optimize noise cancellation for specific configurations, then noise cancellation performance is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by making only the feedback gain adaptive while keeping the canceling filter structure fixed. This localized adaptation approach allows the system to optimize performance for different configurations without requiring the entire filter to be complex and adaptive. By adjusting only the gain parameter based on the secondary path characteristics, the system achieves configuration-specific optimization with minimal increase in device complexity.
3Reliability
If the feedback gain is increased to ensure stability across all secondary path variations, then system stability is improved, but the noise cancellation effectiveness deteriorates due to suboptimal performance
Solution Approach 1:
The patent applies parameter changes by adjusting the feedback gain parameter based on the measured or estimated secondary path transfer function. Instead of using a fixed high gain for all configurations, the system modifies the gain parameter to match the actual operating conditions. This allows the system to use lower, more optimal gains when the secondary path characteristics permit, thereby improving noise cancellation effectiveness while maintaining stability.
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
This approach results in a more efficient and high-performance noise canceling system with improved adaptability to different configurations, maintaining low complexity and optimizing noise cancellation by dynamically adjusting the feedback loop gain in response to secondary path changes.
Implementation Method 1
the noise cancellation signal seeks to provide a signal with an opposite phase of the sound wave arriving at the microphone thereby resulting in a destructive interference that at least partly cancels out the noise in the audio environment
Implementation Method 2
a microphone sensing the audio environment typically close to the users ear (e.g. within the acoustic volume created by the earphones around the ear)
Data Source
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AI summary
A noise canceling system comprises a microphone (103) generating a captured signal and a sound transducer (101) radiating a sound canceling audio signal in the audio environment. A feedback path (109) from the microphone (103) to the sound transducer (101) comprises a non-adaptive canceling filter (115) and a variable gain (117) and receives the captured signal and generates a drive signal for the sound transducer (101). A gain detector determines a secondary path gain for at least part of a secondary path of a feedback loop. The secondary path may include the microphone (103), the sound transducer (101), and the acoustic path therebetween but does not include the non-adaptive canceling filter (115) or the variable gain (117). A gain controller (121) adjusts the gain of the variable gain (117) in response to the secondary path gain. The system uses simple gain estimation and control to efficiently compensate for variations in the secondary path to provide improved stability and noise canceling performance.