Design a Filter using the Digital FIR Filter.vi

Question

Hello,
I was working with Digital FIR Filter.vi to create a bandstand filter.
The problem I faced is regarding the FIR Filter Specification, the Frequencies given for the Upper and Lower Pass and Stop band.
For a low pass Filter, the upper Stop Band frequency is set at 0. While the Lower Stop band frequency is set at 200.
And the Lower pass band is set at 100 while the upper pass band is set at 0.
What the lower and upper frequencies actually means? As for a low pass filter, the upper cutoff frequency must be greater than lower. 
So plus tell me how does it works and what frequencies should I specify for a Bandstand Filter.
Thanks v.much

Answer 1

Hi,
Have a look at the following example: [LabVIEW Folder]\examples\Digital Filter Design\Floating-Point Filters\Conventional\Classical Filter Design.vi .This example demonstrates how to use the DFD Classical Design VI to design a lowpass, highpass, bandpass, or bandstop filter with classical design methods.
Complete the following steps to use this VI.
1) Run the VI.
2) Change the specifications.
3) Observe the magnitude response and phase response. Notice that the magnitude response approximates the frequency specification and the phase response is nonlinear for IIR filters (Butterworth, Chebyshev, Inverse Chebyshev, and Elliptic).
4) Change the Design Method to view the ripples in the passband and stopband.
5) Observe the filter order that the VI returns automatically.
6) Click the STOP button to stop this VI.
Sev K.
Applications Engineering Specialist | CLA
National Instruments