Period =2in time domain 2. 1and w=0. 1 are the same 05 .5 012345 trigonometric function property -y coa(s'Tan =co2(0 av)
cos(2.1n) = cos(0.1n) Period =2πin time domain： w=2.1πand w=0.1πare the same trigonometric function property
high frequency is changed into low frequency in time domain: w-l. l and w=0are the same 0.5 0 -0.5 10 trigonometric function property co?(r]s)=c02(0)
cos(1.1n) = cos(0.9n) high frequency is changed into low frequency in time domain： w=1.1π and w=0.9πare the same trigonometric function property
2. ideal reconstruction D/C Figure 4.10(b) ideal D/C converter
2.ideal reconstruction Figure 4.10(b) ideal D/C converter
ideal reconstruction in frequency domain Xeon) Xso) >2N 2 Hr(n) N<<(23-N) F1 gur 4 X()
Figure 4.4 ideal reconstruction in frequency domain = s / 2
EXAMPLE Figure 4.5 Take sinusoidal signal for example to understand aliasing from frequency domain X(j9) X、(j9) No aliasing 丌丌 X、(j) 40 ↑,↑ .-9 (3-)(23-)
EXAMPLE Figure 4 . 5 Take sinusoidal signal for example to understand aliasing from frequency domain s − 0