Digital Signal Processing Reference
In-Depth Information
+f
-f
0
-f
+f
+f
-f
Illustration 87:
Symmetrical spectrum
Top: representation of a (periodic) rectangular pulse with the pulse duty factor t/T = 1/10 in the time and
frequency domain. The amplitudes of the first 9 harmonics point upwards on the "playing field" of sinusoi-
dal signals at the centre of the pulse (t = 0.5 s) in the direction of the pulse, the next 9 harmonics by
contrast point downwards etc. Bottom: representation of the amplitude spectrum (of a one-off, i.e. non-
periodic rectangular pulse) with negative frequencies and amplitudes. A "symmetrical FOURIER transfor-
mation" from the time to the frequency domain and vice versa now results. Note that now the phase
information is also contained in the amplitude spectrum.
