How to calculate the frequencies interval?

As showed below, how to calculate the frequencies interval in the red box?

Answer 1

[Cameron]

I'm a little confused what you're asking, but if you have access to the x and y data then you should be able to use the findpeaks function. For example

x = 0:0.01:10; %simulate some time vector in seconds
y = sin(2.22*x); %simulate some y data
[~,loc] = findpeaks(y); %find peaks. You can check the documentation for additional arguements
plot(x,y,'-',x(loc),y(loc),'o') %plot the data just to see what you're looking at
f = 1/(x(loc(2)) - x(loc(1))); %frequency in Hz