HOW CAN I PLOT A CURVE OVER THE SPECTROGRAM OF A LOGARITHMIC CHIRP

Question

raj 2012-3-9

评论： William Rose 2022-11-27

I want to represent the true frequency of a logarithmic chirp. So I want to plot a curve over the spectrogram plane can you help me with this??

Buba 2022-11-27

See the link below for guide

https://www.mathworks.com/help/signal/ref/spectrogram.html

Answer 1

William Rose 2022-11-27

YOu can follow the spectrogram command with "hold on" and then make additinal plots on the same image.

William Rose 2022-11-27

For example:

t = 0:1/1e3:10; %time vector (s)

f0=10; f1=400; %start, end frequencies (Hz)

y = chirp(t,f0,t(end),f1,'logarithmic');

pspectrum(y,t,'spectrogram') %compute and plot spectrogram of the chirp

ax=gca; ax.YScale = 'log'; %make y axis log scale

Now add a plot of the expected frequency versus time

%Next: compute expected frequency versus time

fexp=f0*exp((t/t(end))*log(f1/f0)); %expected frequency

hold on; plot(t,fexp,'-r') %plot expected freq. vs. time