Spectrogram not completely showing from Audio Signal

Hello I am trying to produce a linear chirp signal that is three seconds long and has a sampling rate (Fs) of 33600. The initial frequency should be 200 Hz and the final frequency be 12,000 Hz. I created a spectrogam for the audio signal but only part of of the results are shown in the spectrogram. Can you please help me solve this problem I'm having?

Fs = 33600;
dt = 0.001;
t = 0:dt:3;
f0 = 200;
f1 = 12000;
t1 = 3;
A = 1;
x = chirp(t,f0,t1,f1);



soundsc(4*x,1/0.001);
plot(t,x)

%%

spectrogram(x,128,120,128,1e3,'yaxis');
colormap jet

set(gca,'LineWidth',1.2,'FontSize',36);
set(gcf,'Position',[2500 100 1550 800]);

ylim([0 12000]);

Answer 1

[Voss]

You say the sampling rate is 33600 (Hz, presumably), but in fact the code uses a sampling rate of 1000 Hz, which is insufficient to accurately represent a chirp going up to 12000 Hz.

Using Fs = 33600 instead of 1000 seems to give a reasonable result:

Fs = 33600;
dt = 1/Fs;%0.001;
t = 0:dt:3;
f0 = 200;
f1 = 12000;
t1 = 3;
A = 1;
x = chirp(t,f0,t1,f1);
% % soundsc(4*x,1/0.001);
% soundsc(4*x,Fs);
plot(t,x) % A lot more samples now:

% spectrogram(x,128,120,128,1e3,'yaxis');
spectrogram(x,128,120,128,Fs,'yaxis');
colormap jet
set(gca,'LineWidth',1.2,'FontSize',36);
set(gcf,'Position',[2500 100 1550 800]);
ylim([0 12]);%000]); % Units are kHz