What the z-axis means from the spectrogram function?

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Wendy Fernandez
Wendy Fernandez 2017-6-12
评论： Star Strider 2017-6-15
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?

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Star Strider
Star Strider 2017-6-12
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.
  2 个评论
Wendy Fernandez
Wendy Fernandez 2017-6-15
编辑：Wendy Fernandez 2017-6-15
Thank you for your explanation. But, I thought z-axis was power in db. Could you explain why is amplitude?
Star Strider
Star Strider 2017-6-15
My pleasure.
‘Amplitude’ is simply a generic term. There are many ways to express it, depending on what you are doing. You are correct that the amplitude in the power spectral density plot is power in dB.

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