V_LIN2PCMA Convert linear PCM to A-law P=(X,M,S) pcma = v_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
0001 function p=v_lin2pcma(x,m,s) 0002 %V_LIN2PCMA Convert linear PCM to A-law P=(X,M,S) 0003 % pcma = v_lin2pcma(lin) where lin contains a vector 0004 % or matrix of signal values. 0005 % The input values will be converted to integer 0006 % A-law pcm vlues in the range 0 to 255 and the XORed with m 0007 % (default m=85). 0008 % 0009 % Input values are multiplied by the scale factor s: 0010 % 0011 % s Input Range 0012 % 0013 % 1 +-4096 0014 % 2017.396342 +-2.03033976 (default) 0015 % 4096 +-1 0016 % 0017 % Input values outside the selected range will be clipped. 0018 % 0019 % The default value of the scale factor is 2017.396342 which equals 0020 % sqrt((1120^2 + 2624^2)/2). This factor follows ITU standard G.711 and 0021 % the sine wave with PCM-A values [225 244 244 225 97 116 116 97] 0022 % has a mean square value of unity corresponding to 0 dBm0. 0023 % 0024 % See also PCMA2LIN, LIN2PCMA, LIN2PCMU 0025 0026 0027 0028 % Copyright (C) Mike Brookes 1998 0029 % Version: $Id: v_lin2pcma.m 10865 2018-09-21 17:22:45Z dmb $ 0030 % 0031 % VOICEBOX is a MATLAB toolbox for speech processing. 0032 % Home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html 0033 % 0034 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 0035 % This program is free software; you can redistribute it and/or modify 0036 % it under the terms of the GNU General Public License as published by 0037 % the Free Software Foundation; either version 2 of the License, or 0038 % (at your option) any later version. 0039 % 0040 % This program is distributed in the hope that it will be useful, 0041 % but WITHOUT ANY WARRANTY; without even the implied warranty of 0042 % MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 0043 % GNU General Public License for more details. 0044 % 0045 % You can obtain a copy of the GNU General Public License from 0046 % http://www.gnu.org/copyleft/gpl.html or by writing to 0047 % Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA. 0048 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 0049 0050 if nargin<3 0051 s=2017.396342; 0052 if nargin<2 m=85; end 0053 end 0054 0055 y=x*pow2(s,-6); 0056 y=(abs(y+63)-abs(y-63))/2; 0057 q=floor((y+64)/64); 0058 [a,e]=log2(abs(y)); 0059 d = (e+abs(e))/2; 0060 p=128*q+16*d+floor(pow2(a,e-d+5)); 0061 if m p=bitxor(p,m); end;