Let H be the vector that is the mathematical result of the FFT, so that Hk is the kth element of the vector. H0 is the DC component, and HN/2 is the Nyquist component. Then:
A.realp[0]
contains H0.
A.imagp[0]
contains HN/2.
For 0 < k < N/2, A.realp[k]
and A.imagp[k]
combined contain Hk. Specifically, A.realp[k]
contains the real part of Hk, and A.imagp[k]
contains the imaginary part of Hk. Equivalently, Hk = A.realp[k]
+ i • A.imagp[k]
.
Some documentation about the vDSP FFTs is here.