[Ifeffit] parseval's theorem and athena

Hello, I would like to use parseval's theorem (as described in a document called: Error Reporting Recommendations: A Report of the Standards and Criteria Committee, Adopted by the IXS Standards and Criteria Committee July 26, 2000 ) to quantify the statistical noise in my spectra. In section 3 (as shown in the attachment), it says that for the formula to work, the forward FT has to be normalized by sqrt(deltak/Pi). (delta k is the spacing of points in k space) What is the normalization used for FFT in athena? if it is not sqrt(deltak/Pi), what is it? how does the parseval theorem formula need to be modified as a function of FT normalization? Many thanks for answers! Regina