Fourier analysis with variable input

No sample workbook provided so try (can't test):

Application.Run "ATPVBAEN.XLAM!Fourier", Worksheets("Red").Range(Cells(1, i).Address).Resize(rowsize:=128), _
 Worksheets("Analysis - Red").Range(Cells(430, 48 + i).Address), False, False

Notice that "$A1:A128" and "AV430" in the first are string references which are required by RANGE(). Cells(r,c).Address returns the string that Range is expecting.