Why Is My Filtered Signal Attenuated?

Updated Jan 16, 2019

Reported In


  • LabVIEW Full
  • LabVIEW Professional

Issue Details

I am using the FIR Windowed Filter VI in LabVIEW and although my output signal is clean, the amplitude is significantly smaller than that of my input signal. Why?


Refer to the attached response curve, which is a typical response curve of an FIR low-pass filter. If your filtered signal appears to be attenuated, it is falling within the Transition Region (Tr) of the curve. To solve this problem, you can decrease the sampling rate of your signal. This causes its frequency (in Hz) to decrease, which sends it back up the curve and into the flat high-response region. You also can increase the cut-off frequency of your filter, which moves the Transition Region farther up the frequency scale, giving you a larger range of full response.

Additional Information

Changing the frequency of the filter and the number of taps can also shift the amplitude of the output signal. 


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