gusucode.com > 《MATLAB图像与视频处理实用案例详解》代码 > 《MATLAB图像与视频处理实用案例详解》代码/第 19 章 基于语音识别的信号灯图像模拟控制技术/voicebox/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 % Version: $Id: lin2pcma.m,v 1.4 2007/05/04 07:01:38 dmb Exp $ % % VOICEBOX is a MATLAB toolbox for speech processing. % 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 % http://www.gnu.org/copyleft/gpl.html 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;