I would like to see the spectrogram of x=cos(-250*pi*t^2) for 0<t<2s. How do I plot the spectrogram ( f on y axis, time on x axis)?t = [0,0.1,2]; % Intervall for t y = cos(-2

I need a simple code to plot the spectrogram of sinusoids as f over time.

So far, my code looks like this:

t = [0,0.1,2]; % Intervall for t

y = cos(-250 * pi * t.^2); % the signal

spectrogram(y,t)

But the spectrogram is strange.

Which parameters do I need to add or change?

Answer 1

[Star Strider]

The frequency of the sine curve is 125 Hz, however the sampling frequency of ‘t’ is 10 Hz. This leads to asliasing and unfortunate results. Increase the sampling frequency to 1 kHz and the result appears to be more appropriate —

t = [0:0.001:2]; % Intervall for t
y = cos(-250 * pi * t.^2 ); % the signal
spectrogram(y,t)
colormap(turbo)

I also changed the colormap to make the differences easier to see.

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Answer 2

[Julia-Alexandra Giesbrecht]

Thank you!! When t = [0:0.0005:2] it looks like i want it to. :)

[Star Strider]

As always, my pleasure!

The important change is providing the high sampling rate (2000 Hz) with that ‘t’ vector.

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