Consider a sampled signal with the DTFT
Xω
X
ω
shown in Figure 1.
Assuming
U=D=3
U
D
3
, use the relations between the DTFT of a signal
before and after sample-rate compression and expansion
(Equation 1 and Equation 2) to sketch
the DTFT response of the signal as it passes through the
multirate system of Figure 2 (without any
filtering). Include both the intermediate response
Wω
W
ω
and the final response
Yω
Y
ω
. It is important to be aware that the translation
from digital frequency
ω
ω to analog frequency depends on the sampling rate.
Therefore, the conversion is different for
Xω
X
ω
and
Wω
W
ω
.
Wω=1D∑
k
=0D−1Xω+2πkD
W
ω
1
D
k
0
D
1
X
ω
2
k
D
(1)
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