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Creating and Using Adaptive Filters (Adaptive Filter Toolkit)

LabVIEW 2013 Adaptive Filter Toolkit Help

Edition Date: June 2013

Part Number: 372357B-01

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The LabVIEW Adaptive Filter Toolkit provides the Adaptive Filters VIs that you can use to create, simulate, use, and destroy adaptive filters. You also can analyze the performance of the adaptive filters to ensure that they meet the application requirements. The following steps show a typical procedure that you can follow to create and use an adaptive filter.

  1. Create the adaptive filter by using the appropriate algorithm and specifying the appropriate filter length, step size, and other parameters that the specific algorithm requires.
  2. Use the AFT Filter Signal and Update Coefficients VI to simulate the adaptive filter. If the adaptive filter is a filtered-x LMS adaptive filter, use the AFT Filtered-X Filter Signal and Update Coefficients VI to simulate the filter. After simulating the filter, you can use the filter in real-world applications.
    Note  Do not wire one adaptive filter to two AFT Filter Signal and Update Coefficients VIs at the same time. Instead, create separate adaptive filters and wire each of them to the corresponding VI. For example, LabVIEW returns errors if you use the AFT Filter Signal and Update Coefficients VI as the following figure shows:

    To resolve this problem, create an adaptive filter for each AFT Filter Signal and Update Coefficients VI, as shown in the following figure:

  3. (Optional) Use the AFT Get Coefficients VI to retrieve the coefficients of the adaptive filter. If the adaptive filter is a filtered-x LMS adaptive filter, use the AFT Get FIR Filtered-X Coefficients VI to retrieve the filter coefficients.
  4. Use the AFT Destroy Adaptive Filter VI to destroy the adaptive filter after you filter a signal. If the adaptive filter is a filtered-x LMS adaptive filter, use the AFT Destroy Filtered-X Adaptive Filter VI to destroy the adaptive filter. If you do not destroy the adaptive filter, memory leaks might occur.
    Note  Do not use the adaptive filter after you destroy the filter. For example, the AFT Get Coefficients VI in the following figure might not work.

    In the previous figure, LabVIEW might destroy the adaptive filter before the AFT Get Coefficients VI retrieves the filter coefficients. To resolve this problem, wire the AFT Get Coefficients VI as shown in the following figure:

National Instruments recommends that you create and destroy adaptive filters outside loop structures. However, if you must create an adaptive filter in a loop, you must destroy the adaptive filter in the same loop. Memory leakage occurs if you create an adaptive filter in a loop but destroy the adaptive filter outside the loop, as shown in the following figure:

The previous block diagram creates ten filters but destroys only the last one. To avoid memory leakage, place the AFT Destroy Adaptive Filter VI in the same loop in which you create the adaptive filter, as shown in the following figure:


 

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