Hi Schmidt/Olaf,

Thanks for the update, but I'm still getting same results ? Still have a black notch in my spectrum and noise on the wav ? just like the images I posted before?

I'm only using the ButterWorth class, so I'm using it by:

Code:
Dim kk As New cButterWorth
kk.FilterType = FilterLowPass
kk.Freq = 1000     'EditWAV.SamplingFreq / 4
kk.SampleRate = EditWAV.SamplingFreq
kk.Order = 4

kk.Filter EditWAV.WavData, True

refreshData True