Select samples from plot

Hey to all, this is probably very easy, but im struggling with it, thanks in advance. I have the spectrum of a signal represented in the image above. I need to select samples from x axis(frequency) where y axis is superior to -140dB.

Basiccaly I want two things, select the samples from x where y is superior to -140 and select y samples where y is superior to -140. I was thinking of using the find function, right?

Answer 1

[KSSV]

Let f be your x-axis i.e. frequency values and s be your y-axis i.e. specturm values.

idx = s > -140 ;
x1 = x(idx) ; 
s1 = s(idx) ;