Hi all, I'm now designing a filter with particular shape by using NI Digital Filter Design provided in Signal Processing Toolset. I use the Arbitrary FIR Filter Dsesign with my frequency response data file to build the filter and use it in LabVIEW. However, when I put the filtered signal to calculate THD by using Harmonic Distortion Analyzer.vi, the result was larger that the correct value. I found that when I increase the filter order, the actual frequency response become the desired response but the THD result is also increased. I tried to use 500 as the filter order and each harmonic level was quite simular to the correct level, but the THD value was wrong. Are there any suggestions?
Bill
