FFT法:以圆周卷积代替线性卷积 N=2"≥M+L-1 x(n)0≤n≤L-1 x(n 0L≤n≤N-1 h(n)=h(n)0≤n≤M-1 0M<n<N-1 y(n=x(n)*h(n)=x(n)h(n) H(h)= FFT[h(nN/2*log2 N 2)X(k)=FFTIx(nN/2*log2N 3)Y(k)=H(k)X(k) N 4)(n)=IFFT[Y( N/2*log2N mp=N(+3/2*log, N)FFT法：以圆周卷积代替线性卷积 2 1 m 令 N   M  L  ( ) 0 1 ( ) 0 1 x n n L x n L n N           ( ) 0 1 ( ) 0 1 h n n M h n M n N           2 (1 3/ 2*log ) mF  N  N 1) H(k) = FFT [h(n)] N /2*log2N 4) y(n) = IFFT [Y(k)] N /2*log2N 3) Y(k) = H(k)X(k) N 2) X(k) =FFT [x(n)] N /2*log2N 则 y(n)  x(n)*h(n)  x(n) N h(n)