Noise-Canceling Headset Filter Architecture for Low-Latency ANC
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Solution Overview
Problem
Existing noise reduction systems in audio headsets face challenges in maintaining effective noise cancellation at both low and high frequencies due to limitations in filter adaptation and latency, particularly with Finite Impulse Response (FIR) and Infinite Impulse Response (IIR) filters, leading to reduced performance.
Innovation Solution
An audio headset with an open-loop main noise reduction processing filter connected to an external microphone, combined with a feedback loop and elementary filters, uses adaptive gain control and energy detection to optimize noise reduction across frequencies, including a compensation filter for internal microphone signals and a closed-loop noise reduction feedback loop to enhance attenuation at the eardrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If FIR filters are used for adaptive noise reduction processing, then the filter is easy to adapt, but the latency increases and noise reduction performance is reduced
Solution Approach 1:
The patent changes the fundamental parameter of the filter type from FIR to IIR, which fundamentally alters the filter's impulse response characteristics. IIR filters achieve the same adaptability through different mathematical structures (recursive equations) that require fewer taps and produce lower latency while maintaining adaptive capabilities through coefficient adjustment
2Reliability
If the bandwidth of parallel filters is reduced to avoid high frequency noise amplification, then the algorithm stability improves, but the noise reduction bandwidth is limited
Solution Approach 1:
The patent applies different characteristics to different frequency ranges by using multiple IIR filters with complementary transfer functions. One filter handles low frequencies with high adaptability while another handles high frequencies with stability, and their outputs are combined to achieve broad bandwidth coverage without amplifying high frequency noise
Solution Approach 2:
The patent creates a composite filter system by combining multiple IIR filters with different transfer function characteristics. This composite structure integrates the advantages of each individual filter (low frequency adaptability and high frequency stability) to achieve both algorithm stability and broad noise reduction bandwidth simultaneously
3Adaptability or versatility
If adaptive filtering is used to account for leaks from headset fitting, then the processing chain is modified over time, but the high frequency noise is amplified at the eardrum
Solution Approach 1:
The patent changes the filter type from FIR to IIR, which fundamentally alters how adaptation is achieved. IIR filters use recursive structures with feedback that provide smoother parameter changes over time, preventing the high frequency noise amplification issue while maintaining the ability to adapt to headset fitting leaks through coefficient adjustment
Data Source
AI summary
The headset includes an electro-acoustic transducer, at least one noise reduction processing chain including external and internal microphones, a processing filter including mounted in parallel between the external microphone and an adder, at least one elementary filter each including a recursive filter and an elementary variable gain amplifier, a control unit for the gain of each elementary amplifier according to a signal coming from the external microphone and an error signal coming from the internal microphone.The processing filter includes an open-loop main filter connected at the input to the external microphone and the output of which is connected, to the adder, and to the input of the or each elementary filter.