x1(0)=x(0) X1(0) X(0) x(1)=x(2) (1) X(1) 2 点 x1(2)=x(4) K1(2) X(2) DFT x1(3)=x(6) X1(3) X(3) x2(0)=x(1) (0) X(4) J x2(1)=x(3) Xa(1) 点 X(5) x2(2)=x(5) (2) DFT i X(6) x2(3)=x(7) X2(3) X(7) 图4-2按时间抽选,将一个N点DFT分解为两个M2点DFT