# Interpretation of fft plot

I am trying to understand how to interpret a spectrogram image plot: (1) what does the yellow band and its corresponding color code with a high positive value indicate? There are so many yellow bands in comparison to blue. The legend shows that the yellow bands have higher positive values, so is that higher frequency?

(2) I used the following code to generate the spectrogram. The X axis contains 50 data points because the method splits the signal into segments of length 50. I arbitrary used 10 into the spectrogram function. Is there a specific rule as to how to determine the number of points?

x(1) = rand;
for n = 1:500
x(n+1) = 4*x(n)*(1-x(n));
end

specto=spectrogram(x,10,0,256); %using 256 fft points with no overlap

logspecto=(20*log10(abs(specto)));


• Thank you very much for your answer. Could you please clarify few points based on your answer?(1) the legend shows values 10 to -50...where the range $\pm 10$ corresponds to yellow color. So does high power in low freq indicate more information is conveyed by lower freq? I mean what is useful? High freq or low freq? (2) more samples give finer freq resolution -- is that preferred and why – Sm1 Jul 15 at 3:27