Scipy Spectrogram vs Matlab Spectrogram

Question

As in my last question AttributeError: 'module' object has no attribute 'spectrogram', I'm writing a little python script which reads a Wav Audio File, computes the spectrogram and writes the corresponding data back into a Wav File again. Here's a bit of code:

Scipy Code:

windowSize = 512
nOverlap_py = 160
nFFT = 1024

Fpy,Tpy,Spy=signal.spectrogram(s_orig_py,fs=fs_rate,window='hamming',nperseg=
windowSize,noverlap=nOverlap_py,nfft=nFFT,detrend=False,mode='complex')

The First 10 Elements of Scipy:

The Last 10 Elements of Scipy:

Matlab Code:

[S,F,T] = spectrogram(s_orig,window,nOverlap,fftParams.nFFT,fs);

The First 10 Elements of Matlab:

The Last 10 Elements of Matlab:

In both cases the parameters are the same. There is just a little problem: The values of Spy are not even close to the values of S and I don't understand why. I get that they can't be identical due the fact that both functions use a different algorithm to compute the FFT but as I mentioned before they are not even close.

Furthermore with Matlab, the resulting Wav File sounds 'exactly' the same as the original. With python it's just noise.

scipy defaults `return_onesided` to `True`. Try setting to `False` and see what you get. — Mad Physicist, Apr 12 '17 at 16:48
If I understand correctly, setting `return_onesided` to `False` will basically return the FFT, which is what MATLAB does. Otherwise you chop everything before the nyquist frequency off. — Mad Physicist, Apr 12 '17 at 16:50
If my suggestion works, I'll write up an answer for you to accept. — Mad Physicist, Apr 12 '17 at 16:51
@MadPhysicist: Unfortunately I get the same results as before. — Nico, Apr 12 '17 at 17:41
Also, can you print out the first 10 and last 10 elements of each input array for both platforms? — Mad Physicist, Apr 12 '17 at 17:44
@MadPhysicist: If I try to play back the result in Python, there's actually nothing respectively noise. And Before I write the data back into an audio file, I have to perform the IFFT with an Overlap Add Procedure. — Nico, Apr 12 '17 at 18:21
@Mad Physicist: Those are the original inputs and outputs from scipy and matlab. Both matrices have a dimension of 513x390 — Nico, Apr 14 '17 at 18:36

score 0 · Answer 1 · answered Sep 06 '17 at 04:02

Before answering your question, may I ask you which library are you using to read a wav input scipy.io.wavfile?

Actually, I recently came across this mismatch in values and back traced the problem to scipy.io.wavfile

In Matlab, usually audioread(fname) is used. The equivalent read library is pySoundfile as given in this post. (Also i used it and got same matrices from Matlab and Python) How to read a audio file in Python similar to Matlab audioread?

Scipy Spectrogram vs Matlab Spectrogram

1 Answers1