# Relation between spectral leakage and the frequency of harmonics of a signal

I'm currently studying "Data Acquisition".

I read that when we have frequency/spectral resolution equal to a natural number, there will be no spectral leakage, for none of the harmonics.

However the text I read makes a parenthesis about a situation where the harmonics frequency is greater than half the sampling frequency but it doesn't explain on detail what happens. I was wondering if someone could give me some explanation please.

I'm also testing this phenomena on lab.

On one experiment I'm sampling a triangular signal with frequency 600 Hz and sampling frequency 24000 with 5600 samples. I'm studying the first 11 harmonics. In this case 11*600= 6600<12000 so I assume no spectral leakage.

On the other hand I have a square wave with frequency 500 Hz and sampling frequency 9500 with 1710 samples. I'm studying again the first 11 harmonics and then again theoretically we would have no spectral leakage. However in this case the 10th and 11th harmonic will have a frequency greater than fs/2 so spectral leakage?

But now that I think about it, while I was writing this. Isn't f>fs/2 a condition for aliasing? So I'm getting aliasing instead of spectral leakage. I'm confused.

• no, that's not spectral leakage, that's aliasing. You're right about that! Nothing much to explain about that – if you understand aliasing, you're understanding what happens to the harmonics that end up at or above $f_s/2$. Nov 6, 2019 at 21:02