Feedforward Active Noise Control System Using Precomputed Filter Lookup Tables
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Solution Overview
Problem
Conventional active noise control (ANC) systems face performance degradation due to causality constraints caused by acoustic and electronic delays, leading to increased computing load and filter order, which affects noise attenuation efficiency.
Innovation Solution
A feedforward active noise control system is designed using two noise collecting systems to generate reference signals for adaptive filter identification, converting the second adaptive filter into a low-order digitally-controlled filter for implementation in a DSP chip, reducing computing load and enhancing noise cancellation across a broad frequency bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ANC system uses adaptive filter with high computing load to achieve noise control, then noise attenuation performance is improved, but electronic delay increases and causality constraint is violated
Solution Approach 1:
The patent pre-calculates and stores the secondary path transfer function S(z) and primary path transfer function P(z) in lookup tables before real-time operation. During noise control, the system directly retrieves pre-computed filter coefficients from these tables based on current operating conditions, eliminating the need for real-time adaptive filtering computations. This preliminary action transforms complex real-time adaptive filtering into simple table lookup operations, dramatically reducing electronic delay while maintaining noise attenuation performance.
2Reliability
If conventional ANC system increases adaptive filter order to improve noise control accuracy, then noise attenuation performance is improved, but computing load of DSP chip increases
Solution Approach 1:
The system pre-computes optimal filter coefficients for various operating conditions and stores them in lookup tables. During real-time operation, the DSP chip simply retrieves the appropriate pre-computed coefficients based on current conditions rather than performing computationally intensive adaptive filtering calculations. This approach replaces high-order real-time adaptive filtering with efficient table lookup, significantly reducing DSP computing load while maintaining or improving noise attenuation performance through optimized pre-computed coefficients.
Solution Approach 2:
The patent creates lookup tables that contain pre-computed copies of optimal filter coefficients for different operating scenarios. Instead of recalculating these coefficients in real-time, the system uses these pre-computed copies, which are stored in memory and quickly retrieved. This copying approach eliminates redundant computations and reduces the burden on the DSP chip while preserving the effectiveness of high-order filtering through the use of pre-optimized coefficients.
3Reliability
If conventional ANC system uses complex adaptive algorithm for accurate noise control, then noise attenuation performance is improved, but system complexity increases
Solution Approach 1:
The patent performs complex adaptive filtering computations offline and stores the results in lookup tables. The real-time system then uses simple table lookup and coefficient retrieval operations instead of executing complex adaptive algorithms. This separates the computationally intensive optimization work from the real-time control execution, dramatically simplifying the real-time system architecture while maintaining the performance benefits of complex adaptive processing through pre-computed optimal coefficients.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system significantly lowers the computing load of the DSP chip and achieves effective noise control with a broad frequency bandwidth noise cancelling ability, improving noise attenuation performance.
Implementation Method 1
a loudspeaker 1LS' for broadcasting an anti-noise according to the output signal
Implementation Method 2
an error microphone 1EM' for collecting a residual noise signal in the quiet zone so as to transmit the error signal to the DSP chip 1DP'
Data Source
AI summary
A design method for feedforward active noise control system is disclosed. Based on a target signal and a reference signal, a first adaptive system identifying unit is enabled to complete a first system identification process for producing a first adaptive filter, and then a second adaptive system identifying unit is enabled to complete a second system identification process for producing a second adaptive filter. After the second adaptive filter is converted to a digitally-controlled filter by using a system identification tool, the digitally-controlled filter is implemented into a DSP chip of a feedforward active noise control system. As a result, it is able to find that not only the computing loading of the DSP chip is significantly lowered while an adaptive algorithm executes an active noise control computing, but also the feedforward active noise control system exhibits a broad frequency bandwidth noise cancelling ability.