Adaptive High-Pass Filter for Wind Noise Reduction
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Solution Overview
Problem
Existing noise reduction circuits in communications applications, such as those using dynamic high-pass filters and programmable gain amplifiers, either distort audio characteristics or require excessive silicon utilization, failing to effectively reduce low-frequency wind noise while maintaining audio fidelity.
Innovation Solution
An integrated adaptive high-pass filter architecture utilizing existing AC coupling capacitances and programmable resistors, combined with an adaptive equalizer, to suppress low-frequency noise while minimizing input-referred noise and maintaining audio fidelity across a wide dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dynamic high-pass filter is used to reduce low-frequency wind noise, then wind noise reduction is improved, but audio fidelity deteriorates due to pole distortion within the audio band
Solution Approach 1:
The patent implements a dynamic high-pass filter where the cutoff frequency is adaptively adjusted based on the detected wind noise level. When wind noise is detected, the filter dynamically shifts poles to attenuate low-frequency noise; when wind noise is absent, the filter returns to a flat response to preserve audio fidelity. This dynamic adaptation resolves the contradiction by providing noise reduction only when necessary.
Solution Approach 2:
The patent changes the filter parameters (pole positions and cutoff frequency) based on the detected noise conditions. By monitoring the noise floor and adaptively adjusting the high-pass filter characteristics, the system achieves effective wind noise suppression while maintaining natural audio reproduction during normal conditions, thus resolving the fidelity-distortion problem.
2Manufacturing precision
If a brick-wall high-pass filter is used to maintain flat audio response, then audio fidelity is improved, but device complexity and component requirements worsen due to high filter order demands
Solution Approach 1:
Instead of using a static high-order brick-wall filter, the patent employs a dynamic filter that adapts its characteristics based on noise conditions. This allows the use of a lower-order filter that achieves effective wind noise suppression only when needed, eliminating the need for complex high-order filtering circuitry while maintaining audio fidelity during normal operation.
Solution Approach 2:
The patent dynamically changes filter parameters (cutoff frequency and pole positions) based on detected noise levels. This adaptive approach replaces the need for a fixed high-order brick-wall filter with a lower-order dynamic filter that provides equivalent performance only when wind noise is present, significantly reducing component requirements and circuit complexity.
3Reliability
If a programmable gain amplifier is used to reduce gain during wind noise, then clipping is avoided, but input-referred noise increases and signal range is reduced
Solution Approach 1:
The patent extracts the wind noise component from the audio signal using adaptive spectral analysis and removes it through dynamic filtering before the signal reaches the PGA. By eliminating the low-frequency noise early in the signal chain, the system avoids the need to reduce PGA gain, thereby preventing the increase in input-referred noise that would otherwise occur.
Solution Approach 2:
The patent performs preliminary wind noise suppression through adaptive high-pass filtering before the signal enters the PGA stage. By pre-processing the signal to remove wind noise components, the system prevents clipping without requiring gain reduction, thus avoiding the penalty of increased input-referred noise and preserved signal range.
Data Source
AI summary
A noise reduction circuit for reducing the effects of low frequency noise such as wind noise in communications applications is described. In one embodiment, the noise reduction circuit features a high pass filter formed by exploiting the existing off-chip AC coupling capacitances in making the connection to the source of audio signals. The filter may be adaptive to environmental low frequency noise level through programming the shunt resistances. A low-noise wide dynamic range programmable gain amplifier is also described. Adaptive equalization of the audio signal is also described through the utilization of programmable front-end resistors and a back-end audio equalizer.