import matplotlib.pyplot as plt
import numpy as np
from scipy.fftpack import fft

def save_fft(sig, sample_spacing_s, filepath):
    # Where is the dependency on time?
    f = fft(np.array(sig))

    plt.figure()
    plt.xlabel('Frequency [Hz]')
    plt.ylabel('Magnitude []')
    plt.savefig(filepath)