www.pudn.com > voicebox2.zip > LIN2PCMA.M

function p=lin2pcma(x,m,s) 
%LIN2PCMA Convert linear PCM to A-law P=(X,M,S) 
%	pcma = lin2pcma(lin) where lin contains a vector 
%	or matrix of signal values. 
%	The input values will be converted to integer 
%	A-law pcm vlues in the range 0 to 255 and the XORed with m 
%	(default m=85). 
%	 
%	Input values are multiplied by the scale factor s: 
% 
%		   s		Input Range 
% 
%		   1		+-4096 
%		2017.396342	+-2.03033976 (default) 
%		4096		+-1 
% 
%	Input values outside the selected range will be clipped. 
% 
%	The default value of the scale factor is 2017.396342 which equals 
%	sqrt((1120^2 + 2624^2)/2). This factor follows ITU standard G.711 and 
%	the sine wave with PCM-A values [225 244 244 225 97 116 116 97] 
%	has a mean square value of unity corresponding to 0 dBm0. 
% 
%	See also PCMA2LIN, LIN2PCMA, LIN2PCMU 
 
 
 
%      Copyright (C) Mike Brookes 1998 
% 
%      Last modified Thu May 14 14:54:50 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. 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
if nargin<3 
  s=2017.396342; 
  if nargin<2 m=85; end 
end 
 
y=x*pow2(s,-6); 
y=(abs(y+63)-abs(y-63))/2; 
q=floor((y+64)/64); 
[a,e]=log2(abs(y)); 
d = (e+abs(e))/2; 
p=128*q+16*d+floor(pow2(a,e-d+5)); 
if m p=bitxor(p,m); end;