CODEWITHSUNDEEP
pythonmatlabscipyspectrogram
jukebox41188
jukebox41188

Reputation: 25

Python Scipy Spectrogram

I am trying to plot the spectrograms of some .wav files.

I originally implemented it in Matlab, and my plot makes sense.

Matlab code:

sound = audioread(x); 
[S, F, T] = spectrogram(sound(:,1),1000,500,1000,48000); %get channel 1
S_dB = mag2db(abs(S));
%disp(S_dB)


%play sound
[y, fs] = audioread(x);
player = audioplayer(y, fs);
play(player);

%plot figure
figure;
imagesc(T, F, S_dB);
axis xy;
title(x,'Spectrogram');
xlabel('Time (s)');
ylabel('Frequency (Hz)');
colorbar;

Matlab plot: matlab spectrogram plot

I am trying to move my code over to Python, so I am using scipy. I have the following:


    rate, data = wavfile.read(file)
    #from Matlab: spectrogram(X = sound(:,1), WINDOW = 1000, NOVERLAP = 500,F = 1000,Fs = 48000)
    f, t, Sxx = signal.spectrogram(data, fs=48000, window=('hamming'), nperseg=1000, noverlap=500, nfft=1000, detrend = 'constant', return_onesided=True, scaling='density', axis=-1, mode='psd')
    dB = control.mag2db(np.abs(Sxx)) #get magnitude of signal and convert to dB
    plt.pcolormesh(t, f, dB, shading='gouraud')
    plt.ylabel('Frequency [Hz]')
    plt.xlabel('Time [sec]')
    plt.colorbar()
    plt.title(file) #V up, V down, H up, H down
    plt.show()

When I plot it in Python, I get this: Python Spectrogram plot

I took these recordings on a recorder with a relative max dB at -0 dB, so I know the Matlab file is right. I am not sure how to fix it in the Python file.

The S that is returned from the spectrogram file in Matlab is made up of complex numbers, and the Sxx that is returned in Python are real numbers (that differ from the real parts of the Matlab numbers). I am not sure why these numbers are so different? Any advice helps, thanks!

Upvotes: 1

Views: 265

Answers (1)

bb1
bb1

Reputation: 7873

If you set mode='psd' then scipy.signal.spectrogram returns the square of the magnitude. Thus Sxx should correspond to abs(S) squared.

Upvotes: 0

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