www.gusucode.com > 语音信号处理工具箱 - Voicebox源码程序 > Voicebox\irfft.m
function x=irfft(y,n) %IRFFT Inverse fft of a conjugate symmetric spectrum X=(Y,N) % Y contains FIX(1+N/2) complex samples from the spectrum: if argument N % is specified then Y will be truncated or padded accordingly % IMPORTANT: If N is odd, it MUST be specified explicitly. % % See also RFFT % Copyright (C) Mike Brookes 1998 % % Last modified Fri Apr 3 14:57:14 1998 % % VOICEBOX home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % This program is free software; you can redistribute it and/or modify % it under the terms of the GNU General Public License as published by % the Free Software Foundation; either version 2 of the License, or % (at your option) any later version. % % This program is distributed in the hope that it will be useful, % but WITHOUT ANY WARRANTY; without even the implied warranty of % MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the % GNU General Public License for more details. % % You can obtain a copy of the GNU General Public License from % ftp://prep.ai.mit.edu/pub/gnu/COPYING-2.0 or by writing to % Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% fl=size(y,1)==1; if fl y=y(:); end [m,k]=size(y); if nargin<2 n=2*m-2; else mm=1+fix(n/2); if mm>m y=[y; zeros(mm-m,k)]; elseif mm<m y(mm+1:m,:)=[]; end m=mm; end if rem(n,2) % odd case x=real(ifft([y;conj(y(m:-1:2,:))])); else % even case y(m,:)=real(y(m,:)); % force nyquist element real w=ones(1,k); % t=[cumprod([-0.5i; exp(2i*pi/n)*ones(m-2,1)]); 0.5i]; t=-0.5i* exp((2i*pi/n)*(0:m-1)).'; z=(t(:,w)+0.5).*(conj(flipud(y))-y)+y; z(m,:)=[]; zz=ifft(z); x=zeros(n,k); x(1:2:n,:)=real(zz); x(2:2:n,:)=imag(zz); end if fl x=x.'; end