Working with LabVIEW Filtering VIs and the LabVIEW Digital Filter Design Toolkit VIs

The LabVIEW Digital Filter Design Toolkit contains several filter design tools that are similar to the filtering tools included with the LabVIEW Full or Professional Development System. For example, the Butterworth Coefficients VI in LabVIEW Full or Professional Development System is similar to the Butterworth Design functionality from the Digital Filter Design Toolkit. Also, the Parks-McClellan VI in LabVIEW Full or Professional Development System is similar to the Remez Design VI from the Digital Filter Design Toolkit. 

In general, the Digital Filter Design Toolkit provides greater capabilities including, but not limited to, support for arbitrary phase and magnitude specifications and fixed-point filter design.

Although the two sets of VIs have similar functionality, their results might not be the same because the design algorithms are different. This document explains the major differences between the two sets of VIs, lists the similar VIs, and provides examples that demonstrate how to convert filters designed with the LabVIEW Full or Professional Development System for use in the Digital Filter Design Toolkit and vice versa.

The following list explains the main differences between the filtering VIs in the LabVIEW Full or Professional Development System and the Digital Filter Design Toolkit.

• The filtering VIs included in the LabVIEW Full or Professional Development System do not provide optimal solutions, except for the Equi-Ripple method. The Digital Filter Design Toolkit contains classical design methods as well as optimal solutions.
• The filtering VIs included in the LabVIEW Full or Professional Development System offer limited phase selections. With the Digital Filter Design Toolkit, you can specify arbitrary magnitude and phase response for any type of filters.
• The outputs of the classical design methods from LabVIEW Full or Professional Development System filtering VIs might be different from the outputs computed from the Digital Filter Design Toolkit because the two sets of VIs use different design algorithms.
• The Digital Filter Design Toolkit supports more filter structures than LabVIEW Full or Professional Development System.
• The FIR Narrowband Coefficients VI in LabVIEW Full or Professional Development System produces at most two-stage filters. The DFD Narrowband Filter Design VI takes advantage of cascaded integrator comb (CIC) filters, with which you can produce three-stage filters. In general, three-stage filters are more efficient than two-stage filters.
• The filtering VIs included in the LabVIEW Full or Professional Development System are coefficients-oriented. The VIs included in the Digital Filter Design Toolkit are object-oriented. Refer to the Examples section below for more information about how to use both sets of VIs in the same application.

The following table lists the names of similar VIs in the LabVIEW Full of Professional Development System and the Digital Filter Design Toolkit. Although the VIs listed in the table have similar functions, their results might not be the same.

Because the filtering VIs in LabVIEW Full or Professional Development System are coefficients-oriented and the DFD VIs are object-oriented, you must use the DFD Utilities VIs to convert filters you designed in LabVIEW Full or Professional Development System to filters you can use with the Digital Filter Design Toolkit. Likewise, you can use the Utilities VIs to retrieve filter information from filters you designed with the Digital Filter Design Toolkit to filter signals you can use with the filtering VIs in LabVIEW Full or Professional Development System.

The following block diagram demonstrates how to apply the coefficients computed for a finite impulse response (FIR) filter in LabVIEW Full or Professional Development System to create a digital FIR filter in the Digital Filter Design Toolkit using the DFD Build Filter from TF VI.
 

The following block diagram demonstrates how to apply the coefficients computed for an infinite impulse response (IIR) filter in LabVIEW Full or Professional Development System to create a digital IIR filter in the Digital Filter Design Toolkit using the DFD Build Filter from Cascaded Coef VI.

The following block diagram demonstrates how to retrieve filter coefficients from a filter you designed with the Digital Filter Design Toolkit using the DFD Get TF VI and then use the coefficients to filter a signal with the IIR Filter VI in LabVIEW Full or Professional Development System.
 

The following block diagram demonstrates how to convert a filter from the Digital Filter Design Toolkit to an IIR filter cluster that is compatible with the IIR Filter Cluster output in the LabVIEW Full or Professional Development System filtering VIs.