Okay I put the file into both plugin32 and plugin64 folder, the 64 bit one is working fine, but the 32 bit give me an error on opening "the procedure entry point fftwf_alloc_real could not be located in the dynamic link library libfftw3f-3.dll".
EDIT: actually the 64 bit is not working fine either, it doesn't have the entry point error on Vapoursynth editor startup, but it return dfttest namespace doesn't exist when I try to run it.
Code:
ret = core.dfttest.DFTTest(ret, sigma=1.5)