fast_fourier_transform2.py

"""another Fourier transform example from I don't remember where"""
from numpy import sin,  pi, arange
from pylab import plot, show,  xlabel, ylabel, subplot
from scipy.fft import fft, ifft

def plotSpectrum(y, Fs):
    """
    Plots a Single-Sided Amplitude Spectrum of y(t)
    """
    n = len(y)  # length of the signal
    k = arange(n)
    T = n / Fs
    frq = k / T  # two sides frequency range
    frq = frq[range(n // 2)]  # one side frequency range

    Y = fft(y) / n  # fft computing and normalization
    Y = Y[range(n // 2)]

    plot(frq, abs(Y), 'r')  # plotting the spectrum
    xlabel('Freq (Hz)')
    ylabel('|Y(freq)|')


Fs = 150.0  # sampling rate
Ts = 1.0 / Fs  # sampling interval
t = arange(0, 1, Ts)  # time vector

ff = 5  # frequency of the signal
y = sin(2 * pi * ff * t)

subplot(2, 1, 1)
plot(t, y)
xlabel('Time')
ylabel('Amplitude')
subplot(2, 1, 2)
plotSpectrum(y, Fs)
show()