Dynamic Cutoff Frequency Speech Filter for Noise Reduction
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Solution Overview
Problem
Selecting an optimal cutoff frequency for a high pass filter in speech encoders to balance the removal of low frequency noise and DC bias while minimizing the loss of speech signal quality is challenging, as high cutoff frequencies remove too much of the speech signal, while lower frequencies leave residual noise.
Innovation Solution
A method and filter that dynamically adjust the cutoff frequency based on parameters such as pitch frequency and signal-to-noise ratio, smoothing the pitch frequency for voiced frames and keeping it constant for unvoiced frames, to attenuate low frequency noise effectively without degrading the speech signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a high pass filter with high cut off frequency is applied to remove low frequency noise, then the removal of low frequency noise is improved, but the speech signal quality deteriorates due to removal of speech components
Solution Approach 1:
The patent applies dynamics by making the filter cutoff frequency adjustable rather than fixed. The system dynamically adapts the cutoff frequency based on the detected pitch frequency of the speech signal, allowing optimal noise removal while preserving speech components. The filter transitions from a static high-pass filter to a dynamic filter that responds to speech characteristics in real-time.
Solution Approach 2:
The patent changes the parameter of cutoff frequency based on the pitch frequency detection. By detecting the pitch frequency of the speech signal and using this information to adjust the filter's cutoff frequency, the system optimizes the balance between noise removal and speech preservation. This parameter adaptation allows the filter to work effectively across different speech conditions.
2Manufacturing precision
If a high pass filter with low cut off frequency is applied to preserve speech signal, then the speech signal quality is maintained, but the removal of low frequency noise is insufficient
Solution Approach 1:
The patent implements feedback by detecting the pitch frequency of the speech signal and using this information to adjust the filter's cutoff frequency. The system continuously monitors the speech signal characteristics and adapts the filter parameters accordingly, creating a closed-loop system that optimizes noise removal while preserving speech quality based on real-time signal analysis.
3Device complexity
If a fixed cutoff frequency is used for the high pass filter, then the device complexity is reduced, but the adaptability to different noise levels and speech signals is insufficient
Solution Approach 1:
The patent applies self-service by enabling the filter system to automatically adjust its own parameters based on the input signal characteristics. The pitch frequency detection mechanism allows the system to self-optimize the cutoff frequency without external intervention, making the filter adaptable to different noise levels and speech conditions while maintaining relatively simple device architecture.
Data Source
AI summary
A method of filtering a speech signal for speech encoding in a communications network, includes determining a cut off frequency for a filter, wherein a component of the speech signal in a frequency range less than the cut off frequency is to be attenuated by the filter; receiving the speech signal at the filter; determining at least one parameter of the received speech signal, the at least one parameter providing an indication of the energy of the component of the received speech signal that is to be attenuated; and adjusting the cut off frequency in dependence on the at least one parameter, thereby adjusting the frequency range to be attenuated.