These spectra have the following characteristics:
- The spectra is periodic with period N .
- The same spectra as those of the negative order
also appear in the range 
. - The spectra of the real part and those of the amplitude are both symmetric about
. - The spectra of the imaginary part and those of the phase are skew symmetric about .
- The spectra in the left half of the zone
are valid. The spectra in the right half are virtual and are too high compared to the sampling frequency. If the sampling interval is narrowed the number of spectra increases, and therefore such a spectra diagram written in the interval 
extends to the right.
For comparison, the spectrum of N = 32 is depicted in Figure 11.27(f) If the sampling frequency is shortened, the sampled data become substantially equal to the continuous wave, and therefore its spectra will approach those of the Fourier series shown in Figure 4.