www.gusucode.com > 语音信号处理工具箱 - Voicebox源码程序 > Voicebox\lpcrf2ar.m
function [ar,arp,aru,g]=lpcrf2ar(rf) %LPCRF2AR Convert reflection coefs to autoregressive coefs [AR,ARP,ARU,G]=(RF) % % Input: RF(:,p+1) gives reflection coefficients of one or more p-section lossless tubes % Ouputs: G is the gain of the all-pole AR filter % AR/G is the transfer function from the output flow to the glottal input wave. % ARP*K is the transfor function from the output flow to the pressure at the glottis % where K = rho*c/Alips: rho = air density 1.23 kg/m^3, c=sound speed 340 m/s, % Alips = effective area of free space beyond the lips. % ARU is the transfer function from the output flow to the total input flow % % Energy into the vcal tract is equal to K*filter(ARP,1,Ulips).*filter(ARU,1,Ulips) % reverse glottal flows divided by 1-r0 where r0 is the glottal reflection coefficient. % The scale factor is included to avoid a zero answer when the glottis is closed giving r0=1. % % The transfer functions have ar(:,1)=art(:,1)=1 % They should both be multiplied by z^(p/2)/prod(1+rf) to correct the absolute % gain and to compensate for the delay of p/2 samples along the length of the tube. % % The energy into the vocal tract is given by ars(speech) * are(speech) % Copyright (C) Mike Brookes 1997 % % Last modified Tue May 12 16:19:13 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. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% [nf,p1]=size(rf); p2=p1+1; p=p1-1; pm=p-1; arf=[ones(nf,1) zeros(nf,p)]; arr=[zeros(nf,p) rf(:,p1)]; cr=zeros(nf,p); for k=1:p-1 rk=rf(:,(p1-k)*ones(1,k)); cr(:,1:k)=arr(:,p2-k:p1); arr(:,p1-k:p)=arr(:,p1-k:p)+rk.*arf(:,1:k); arf(:,2:k+1)=arf(:,2:k+1)+rk.*cr(:,1:k); end r1=rf(:,1); ar=arf+r1(:,ones(1,p1)).*arr; if nargout>1 kp=prod(1-rf(:,2:p1),2); arp=(arf-arr)./kp(:,ones(1,p1)); if nargout>2 g=prod(1+rf(:,2:p1),2); aru=(arf+arr)./g(:,ones(1,p1)); if nargout>3 g=g.*(1+rf(:,1)); end end end