When i plot spectogram with the following code, it shows frequencies at 0.4 and 0.8. Why it is so? Why not 1.256 and 2.51?

N = 1024;
n = 0:N-1;
w0 = 2*pi/5;
x = sin(w0*n)+10*sin(2*w0*n);
s = spectrogram(x);
spectrogram(x,'yaxis')

Answer 1

[Star Strider]

The spectrogram function presents those data because it normalises the frequency axis from 0 to pi. You defined ‘w0=2*pi/5’. Since the arguments to the sin functions are ‘w0’ and ‘2*w0’, the frequencies are 2/5*pi and 4/5*pi, or 0.4 and 0.8 of the full frequency axis range respectively.