Wind Noise Suppression via Frequency-Dependent Spectral Subtraction
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Solution Overview
Problem
Conventional wind noise suppression methods, such as high-pass filtering, spectral subtraction, and comb filtering, fail to effectively suppress low-frequency wind noise components without impairing the audio signal, due to inaccuracies in fundamental tone detection and noise estimation, especially in non-stationary noise environments.
Innovation Solution
A noise suppression apparatus and method that employs spectral subtraction with a noise estimation unit, fundamental tone detection unit, and a factor setting unit to set appropriate subtraction factors, where the boundary frequency is set at or below the fundamental frequency, and larger subtraction factors are applied at frequencies lower than this boundary, to reduce wind noise without affecting the audio signal's tone color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high-pass filtering is used to suppress wind noise, then low-frequency wind noise components are reduced, but fundamental tone and low-order harmonic components of audio signal are also suppressed, changing the tone color of audio
Solution Approach 1:
The patent applies different subtraction factors to different frequency regions. Specifically, a first subtraction factor is applied to frequencies below the fundamental frequency, and a second subtraction factor is applied to frequencies at and above the fundamental frequency. This local differentiation allows aggressive noise suppression in the sub-fundamental region while preserving the audio signal's harmonic structure and tone color.
2Object-affected harmful factors
If spectral subtraction is used with noise estimation, then noise components can be suppressed, but accurate noise estimation is difficult for non-stationary wind noise, leaving noise components unsuppressed
Solution Approach 1:
The patent divides the frequency spectrum into different regions and applies different subtraction factors to each region. By setting the boundary at the fundamental frequency and applying a larger subtraction factor below this frequency, the method achieves effective wind noise suppression without requiring perfectly accurate global noise estimation, thus overcoming the limitation of non-stationary noise characteristics.
3Manufacturing precision
If comb filtering is used with fundamental tone detection, then harmonic structure can be preserved, but detection errors are enlarged in high-frequency range, causing original harmonic structure to be suppressed
Solution Approach 1:
The patent applies spectral subtraction selectively in the frequency domain rather than uniformly across all frequencies. By concentrating the subtraction operation primarily below the fundamental frequency and reducing it at and above the fundamental frequency, the method achieves effective noise suppression while being more tolerant of fundamental tone detection errors, thus preserving the harmonic structure even when detection is imperfect.
Data Source
AI summary
A noise suppression apparatus using spectral subtraction is provided. A noise estimation unit estimates noise components included in a mixed signal. A fundamental frequency of the mixed signal is detected. A subtraction factor in the spectral subtraction is set based on the detected fundamental frequency. The spectral subtraction for the mixed signal is executed using the set subtraction factor and the estimated noise components. A boundary frequency at the fundamental frequency or a frequency lower than the fundamental frequency is set, and a subtraction factor for a frequency lower than the boundary frequency is set to assume a value larger than a subtraction factor for a frequency not less than the boundary frequency.