??:??DFT???

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????DFT???
??????????????? 1. ???????????(?????) 2.
?????????????????? ??????????? 1.
??????????? 2. ?????????????????????????
2
????????????
3
??????
FT
?????
DTFT
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?. ????fc10Hz,????T20ms, ??????? ?
????? ?c 2?fc 20? rad/s ????
?c ?c?T 20? rad/s ? 20 ms
0.4 ? rad
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?9? ???????

1. DFT???
2. DFT?DTFT???
3. DFT??
4. DFT?????????
5. DFT???????

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9.1 DFT???
????????
1. DTFT Discrete Time Fourier
Transform ?????????,?????????,???????????????
2. DFT Discrete Fourier Transform ??????????????
????,??????????????????????
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9.1 DFT???
FT
FS
DTFT
DFS
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9.1 DFT???
??FT?FS?DTFT,???????????,????????,????????????
?????????DFS????????????,?????????????????????????
??????,????????????????????,?????????????????(DFT)
?
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9.1 DFT???
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9.1 DFT???
1) DFT??????DFS
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9.1 DFT???
?????
????
?? ???????
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9.1 DFT???
???
???
??
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9.2 DFT?DTFT???
???????x(n),?DTFT?DFT????????
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9.2 DFT?DTFT???
2) DFT???????????,????????????! ?????2?/N
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(No Transcript)
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?1 ?
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2? N5,
??,
??
???
???????
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(No Transcript)
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????5???
3? N10,
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(No Transcript)
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9.2 DFT?DTFT???
X(k)??X(?)???! ?????2?/N,?N??,X(k) ????X(?)????
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9.3 DFT???
1) ????
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9.3 DFT???
2) ???? (????)
??2?
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9.3 DFT???
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9.3 DFT???
3) ????
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9.3 DFT???
?
?????,
?
?
???
???
???
???
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9.3 DFT???
4)???? (????,????)
N
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4
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9.3 DFT???
3) ??????,DFT??????DTFT
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9.3 DFT???
5) Parseval??
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?????
1. ??
2. ??
??
3. ??
??
N
4. ??
N
5. Parseval??
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9.4 DFT?????????
1) ?????????
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N1N2-110?
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x1(n)
x1(n) x2(n)
x2(n)
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x2(n)
x2(n)
x1((m-n))10
x1(m-n)
4) ?N?N1N2-1,?0,N-1????????????
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9.4 DFT?????????
2) ?DFT??????(??????)
N1
N2
N1 N2 - 1
??NN1 N2 - 1?? DFT
Matlab??
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9.5 ?DFT??????
????????
LPF????? ?????? ?? DFT????
????
????
????
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9.5 ?DFT??????
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9.5 ?DFT??????
??????
? ??????,????????????
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9.5 ?DFT??????
??????
DFT??????????,??????????,??????????????,???
???????????,????????
?
1. N12 2. N24? ??????????DFT?
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9.5 ?DFT??????
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?? 9.2-1 (1)(3)(4), 2 9.3-1 9.5-1,2 9.7-1 (?Matl
ab??????,????????)