I'm trying to understand a paper describing an algorithm for doing autocorrelation of audio signals (so I can implement the algorithm in my C program), and this part of the description confuses me:
As I understand it, xlow and xhigh each represent a finite sequence of (e.g. 1024) audio samples; and DFT is the Discrete Fourier Transform function that I pass the samples into, in order to get back equal-sized sequences of (e.g. 1024) Complex values representing the audio's frequencies-distribution. So far, so good.
The next step, then (as indicated by the vertical bars, if I remember my math notation correctly) is to compute the magnitude/absolute-value of the DFT's. But it's not clear to me what magnitude/absolute-value means in the context of a DFT result. Can someone explain this operation to me (keeping in mind that my mathematical skills are quite rudimentary)?
(Googling only brought me to a bunch of MatLab scripts which invoke the abs() function on a DFT result, but don't describe what the operation does :( )