Subband Adaptive Filter for Partially Acausal Transfer Functions
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Solution Overview
Problem
Existing subband adaptive filters exhibit instability and poor performance when confronted with acausal components in the plant model, leading to uncontrolled growth of coefficients and computational instability.
Innovation Solution
Implement an inverse stacking process to correct coefficients corresponding to acausal components in the plant model, allowing selective activation or deactivation of frequency bands, and incorporating an inverse stacking module to manage coefficient growth and improve convergence rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If subband adaptive filter processes acausal components in the plant model, then coefficient growth becomes uncontrolled and system stability deteriorates
Solution Approach 1:
The patent extracts and removes acausal components from the plant model by identifying coefficients corresponding to negative time delays (tau < 0) and excluding them from the adaptive filtering process. This extraction prevents uncontrolled coefficient growth while maintaining system stability.
Solution Approach 2:
The patent segments the frequency spectrum into multiple subbands and processes each subband separately. By dividing the overall filter into parallel subband filters, each handling a specific frequency range, the system manages coefficient growth more effectively and maintains stability in the presence of acausal components.
2Measurement precision
If subband adaptive filter adapts at full sampling rate, then convergence rate improves, but computational load increases
Solution Approach 1:
The patent implements periodic downsampling of the subband signals at regular intervals rather than continuous full-rate processing. This periodic action reduces the computational load by processing signals at lower rates while maintaining effective convergence through the periodic updates.
Solution Approach 2:
By segmenting the signal into multiple subbands and processing each at a decimated rate, the patent achieves computational efficiency. The segmentation allows parallel processing of multiple lower-rate signals instead of a single high-rate signal, reducing overall computational requirements.
3Reliability
If subband adaptive filter processes all frequency bands, then overall noise cancellation performance improves, but artifacts may affect performance outside target frequency range
Solution Approach 1:
The patent applies local quality by selectively activating or deactivating specific subbands based on the target frequency range. Each subband can be independently controlled to process only the desired frequency components, ensuring high-quality noise cancellation in target bands while avoiding artifacts in non-target bands.
Solution Approach 2:
The patent implements partial action by processing only the frequency bands of interest rather than the entire spectrum. By selectively applying adaptive filtering to specific subbands corresponding to target frequency ranges, the system achieves effective noise cancellation without introducing artifacts in frequencies outside the target range.
Data Source
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AI summary
A noise reduction system includes sensors configured to generate an input signal, an adaptive filter configured to represent a transfer function of a path traversed by the input signal, one or more processing devices, and one or more transducers. The processing devices receive the input signal and generate an updated set of filter coefficients of the adaptive filter by separating the input signal into frequency subbands; determining for each subband, coefficients of a corresponding subband adaptive module; and combining the coefficients of multiple subband adaptive modules. Determining the coefficients of the corresponding subband adaptive module includes selecting a subset of a precomputed set of filter coefficients of the adaptive filter. The processing devices process a portion of the input signal using the updated set of filter coefficients of the adaptive filter to generate an output that destructively interferes with another signal traversing the path represented by the transfer function.