Discontinuities and Fourier series

Again, regarding FT, why is it true that

if the $d$-th derivative is the lowest derivative that contains $\geq 1$ discontinuity then the Fourier coefficients are $O(n^{-(d+1)})$

?

Thanks.

-
Have a look in older question, because I recall having seen this at least two more times. Try with the search engine. –  Giuseppe Negro Sep 20 '11 at 13:07
–  Rajesh D Sep 20 '11 at 13:16
Thanks guys. :-) I am not sure what the variation, V and the primitive period,G. Could someone kindly explain? Thanks again. –  4ier Sep 20 '11 at 13:38
Those 2 terms I mean in the context as in @Christian Blatter's Lemma stated in Giuseppe's link. –  4ier Sep 20 '11 at 13:43