MATLAB: What the z-axis means from the spectrogram function

frequency analysisspectrogram

I am reading the documentation of the spectrogram function and a do not understand a section in specific (Spectrogram and Instantaneous Frequency). The example provided in the documentation is the following:
Fs = 1000;
t = 0:1/Fs:2-1/Fs;
y = chirp(t,100,1,200,'quadratic');
spectrogram(y,100,80,100,Fs,'yaxis')
view(-77,72)
shading interp
colorbar off
The obtained result is the attached image. In the x-axis, the frequency is displayed and z-axis time is displayed, what parameter is displayed in the y-axis?

Best Answer

In image.png, the x-axis is time, the y-axis is frequency (because you told it to plot that way with the 'yaxis' argument), and the z-axis is amplitude.
The spectrogram plot is a surf plot, with the default orientation being ‘view(0,90)’. With ‘view(-77,72)’, you rotated it.
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