CODEWITHSUNDEEP
pythonnumpymatplotlibfft
user3734366
user3734366

Reputation: 69

Got an extra line on python plot

i'm using pyplot to show the FFT of the signal 'a', here the code:

myFFT = numpy.fft.fft(a)
x = numpy.arange(len(a))
fig2 = plt.figure(2)
plt.plot(numpy.fft.fftfreq(x.shape[-1]), myFFT)
fig2.show()

and i get this figure enter image description here

There is a line from the begin to the end of the signal in the frequency domain. How i can remove this line? AM I doing something wrong with pyplot?

Upvotes: 2

Views: 1692

Answers (2)

Guillaume S
Guillaume S

Reputation: 190

Instead of sorted, you might want to use np.fft.fftshift to center you 0th frequency, this deals properly with odd- and even-size signals. Most importantly, you need to apply the transform on both x and y vectors you are plotting.

plt.plot(np.fft.fftshift(np.fft.fftfreq(x.shape[-1])), np.fft.fftshift(myFFT))

You might also want to display the amplitude or phase of the FFT (np.abs or np.angle) - as-is, you are just plotting the real-part.

Upvotes: 3

P. Camilleri
P. Camilleri

Reputation: 13218

Have a look at plt.plot(numpy.fft.fftfreq(x.shape[-1]): the first and last points are the same, hence the graph "makes a loop"

You can do plt.plot(sorted(numpy.fft.fftfreq(x.shape[-1])),myFFT) or plt.plot(myFFT)

Upvotes: 0

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