(0) Compute spectrum of 0kHz 
 Multiply w[n] and a[n] then accumulate vectors.
 w[n] is always w[0] because it's 0kHz.

(1) Compute spectrum of 1kHz 
 w[n] twiddles step by step.
 Find the symmetry of vectors.

(2) Compute spectrum of 2kHz 
 w[n] twiddles but computes by using w[0].
 Later on, it compensates vectors for laglead.

(3) Compute spectrum of 3kHz 
 Computes in the same way as 1kHz.
 Later on, it compensates vectors for laglead.

(4) Compute spectrum of 4kHz 
 4kHz is the Nyquist frequency.
 Gets the spectrum of highest frequency.

(5) Compute spectrum of 5kHz 
 Beyond the Nyquist frequency.
 The spectrum is conjugate with 3kHz.

(6) Compute spectrum of 6kHz 
 Beyond the Nyquist frequency.
 The spectrum is conjugate with 2kHz.

(7) Compute spectrum of 7kHz 
 Beyond the Nyquist frequency.
 The spectrum is conjugate with 1kHz.
