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FFT_DFT.bas

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+Attribute VB_Name = "Module1"
+'Serkan Guer 2023
+'All rights reserved
+Option Explicit
+Type Complex
+   Re As Double
+   Im As Double
+End Type
+'Radix 2 recursive
+Sub F(N As Long, s As Long, q As Long, d As Long, x() As Complex)
+
+   Dim m As Long, p As Long, theta0 As Double
+   Dim wp As Complex, a As Complex, b As Complex
+
+   m = N / 2
+   theta0 = 2 * Application.pi / N
+
+   If N > 1 Then
+      For p = 0 To m - 1
+         wp.Re = Cos(p * theta0)
+         wp.Im = -Sin(p * theta0)
+
+         a = x(q + p)
+         b = x(q + p + m)
+
+         x(q + p).Re = a.Re + b.Re
+         x(q + p).Im = a.Im + b.Im
+
+         x(q + p + m).Re = (a.Re - b.Re) * wp.Re - (a.Im - b.Im) * wp.Im
+         x(q + p + m).Im = (a.Re - b.Re) * wp.Im + (a.Im - b.Im) * wp.Re
+      Next p
+
+      Call F(N / 2, 2 * s, q, d, x)
+      Call F(N / 2, 2 * s, q + m, d + s, x)
+
+   ElseIf q > d Then
+      Call Swap(x(q), x(d))
+   End If
+
+End Sub
+
+Sub Swap(a As Complex, b As Complex)
+   Dim temp As Complex
+   temp = a
+   a = b
+   b = temp
+End Sub
+
+Sub fft(N As Long, x() As Complex)
+   Call F(N, 1, 0, 0, x)
+End Sub
+
+Sub ifft(N As Long, x() As Complex)
+   Dim k As Long
+   For k = 0 To N - 1
+      x(k).Im = -x(k).Im
+   Next k
+
+   Call F(N, 1, 0, 0, x)
+
+   For k = 0 To N - 1
+      x(k).Re = x(k).Re / N
+      x(k).Im = -x(k).Im / N
+   Next k
+End Sub
+
+Sub GenerateFR() 'fast fourier transform
+    Columns("B:H").Select
+    Selection.ClearContents
+    Range("A1").Select
+
+    Application.Calculation = xlCalculationManual
+    Application.ScreenUpdating = False
+
+    Dim N As Long, i As Long, rw As Long, SampleRate As Long, rng As String
+
+    SampleRate = 48000 'Change to correct sample rate
+
+    rw = Range("A1").End(xlDown).Row
+    Dim x(1048575) As Complex
+
+    N = rw
+
+    For i = 0 To N - 1
+       x(i).Re = Cells(i + 1, 1).Value
+       x(i).Im = 0
+    Next i
+
+    Call fft(N, x())
+
+    For i = 0 To N - 1
+       'Cells(i + 1, 2).Value = WorksheetFunction.Complex(x(i).Re, x(i).Im)
+       Cells(i + 1, 2).Value = x(i).Re
+       Cells(i + 1, 3).Value = x(i).Im
+    Next i
+
+    'Extract magnitude and phase
+    Cells(1, 7) = rw
+    Cells(1, 8) = SampleRate
+    Cells(2, 4).Formula = "=sqrt(B2^2+c2^2)"
+    Cells(2, 5).Formula = "=atan2(b2,c2)"
+    Cells(2, 6).Formula = "=F1+$H$1/$G$1"
+    Cells(2, 7).Formula = "=20*LOG10(D2)+100" 'Change 100 to the preferred SPL dB Offset value
+    Cells(2, 8).Formula = "=-180*E2/PI()"
+
+    rng = "D2:H" & rw / 2
+    Range("D2:H2").Select
+    Selection.AutoFill Destination:=Range(rng)
+    Range("G2").Select
+
+    Application.ScreenUpdating = True
+    Application.Calculation = xlCalculationAutomatic
+End Sub
+
+Sub GenerateImpulse() 'inverse fast fourier transform
+    Columns("D:H").Select
+    Selection.ClearContents
+    Columns("A:A").Select
+    Selection.ClearContents
+    Range("B1").Select
+
+    Application.Calculation = xlCalculationManual
+    Application.ScreenUpdating = False
+
+    Dim N As Long, i As Long, rw As Long
+
+    rw = Range("B1").End(xlDown).Row
+    Dim x(1048575) As Complex
+
+    N = rw
+
+    For i = 0 To N - 1
+        x(i).Re = Cells(i + 1, 2).Value
+        x(i).Im = Cells(i + 1, 3).Value
+    Next i
+    'Inverse fft
+    Call ifft(N, x)
+
+    'Write ifft result to column D
+    For i = 0 To N - 1
+        Cells(i + 1, 4) = x(i).Re
+    Next i
+
+    Application.ScreenUpdating = True
+    Application.Calculation = xlCalculationAutomatic
+
+End Sub
+
+Sub dft() 'basic discrete fourier transform
+Dim r As Long, s As Long, k As LongLong, N(1048576) As Double, SumReal As Double, SumImag As Double, pi As Double, w As Double
+Columns("B:H").Select
+    Selection.ClearContents
+    Range("B1").Select
+Application.ScreenUpdating = False
+Application.Calculation = xlCalculationManual
+pi = Application.pi
+
+For r = 1 To 1048576
+    N(r - 1) = Cells(r, 1).Value
+    If Cells(r, 1) = "" Then Exit For
+Next r
+r = r - 1
+
+For k = 0 To (r / 2) - 1
+    SumReal = 0: SumImag = 0
+    For s = 0 To r - 1
+        w = -2 * pi * k * s / r
+        SumReal = SumReal + N(s) * Cos(w)
+        SumImag = SumImag + N(s) * Sin(w)
+    Next s
+    Cells(k + 1, 2) = SumReal: Cells(k + 1, 3) = SumImag
+Next k
+
+Application.ScreenUpdating = True
+Application.Calculation = xlCalculationAutomatic
+End Sub