Redoing the Mathworks fft exercise : https://fr.mathworks.com/help/matlab/ref/fft.html

fft-usage.go

package main

import "github.com/mjibson/go-dsp/fft"
import "math"
import "fmt"
import "math/rand"
import "math/cmplx"

func main() {
    Fs := 1000.0          // Sampling frequency
    T := 1/Fs             // Sampling period
    L := 1000             // Length of signal
    var t, S, X, P2, P1, f []float64
    var Y []complex128

    // build signal+noise
    for i := 0; i < L; i++ {
    	t = append(t, float64(i)*T)
    	S = append(S, 0.7*math.Sin(2*math.Pi*50*t[i]) + math.Sin(2*math.Pi*120*t[i]))
    	X = append(X, S[i] + rand.Float64())
    }
    Y = fft.FFTReal(X)
    // go back to real and take weight into account
    for _, e := range(Y) {
    	P2 = append(P2, cmplx.Abs(e)/float64(L))
    }
    // fold the FFT
    for i, e := range(P2[0:L/2]) {
    	if i == 0 {
	    	P1 = append(P1, e)
    	} else {
	    	P1 = append(P1, 2*e)
    	}
    }
    // build frequencies
    for i := 0; i<L/2; i++ {
	    f = append(f, Fs * float64(i) / float64(L))
    }

    for i, e := range(f) {
        fmt.Println(e, P1[i])
    }
}