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Various spectrograms between MATLAB and Python

I have a program in MATLAB that I want to pass to Python. The problem is that I use the built-in function in it spectrogram, and although the matplotlib function specgramseems identical, I get different results when I run both.

This is the code that I ran.

MATLAB:

data = 1:999; %Dummy data. Just for testing.

Fs = 8000; % All the songs we'll be working on will be sampled at an 8KHz rate

tWindow = 64e-3; % The window must be long enough to get 64ms of the signal
NWindow = Fs*tWindow; % Number of elements the window must have
window = hamming(NWindow); % Window used in the spectrogram

NFFT = 512;
NOverlap = NWindow/2; % We want a 50% overlap

[S, F, T] = spectrogram(data, window, NOverlap, NFFT, Fs);

Python:

import numpy as np
from matplotlib import mlab

data = range(1,1000) #Dummy data. Just for testing

Fs = 8000
tWindow = 64e-3
NWindow = Fs*tWindow
window = np.hamming(NWindow)

NFFT = 512
NOverlap = NWindow/2

[s, f, t] = mlab.specgram(data, NFFT = NFFT, Fs = Fs, window = window, noverlap = NOverlap)

And this is the result that I get in both versions:

http://i.imgur.com/QSPvYsC.png

(In both programs, the variables F and T are the same)

Obviously they are different; in fact, Python execution does not even return complex numbers. What could be the problem? Is there a way to fix this, or should I use a different spectrogram function?

Thank you so much for your help.

+4
1

matplotlib, specgram (mode='PSD '). MATLAB, spectrogram , nargout==4, PSD. matplotlib MATLAB, mode='complex'

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