gusucode.com > 语音信号处理工具箱 - Voicebox源码程序 > Voicebox\schmitt.m
function [y,t]=schmitt(x,low,high) % Pass input signal X through a schmitt trigger % SCHMITT(X,LOW,HIGH) gives low and high thresholds. LOW and HIGH can be % scalars or can be vectors specifiying different thresholds for each X element. % % SCHMITT(X,HYSTERESIS) specifies the thresholds as MAX-DELTA and MIN+DELTA where % DELTA=(MAX-MIN)*(1-HYSTERESIS)/2. % HYSTERESIS must be in the range 0 to 1; default is 0.5. % % Output Y takes values -1, +1 according to whether X<LOW or X>HIGH most recently. % Y may be 0 for an initial segment if neither condition is initially true. % For [Y,T]=SCHMITT(...) Y contains alternate +1 and -1 values and T contains % the sample numbers at which X crossed the thresholds. % Copyright (C) Mike Brookes 1998 % % Last modified Thu Jul 30 08:18:47 1998 % % VOICEBOX is a MATLAB toolbox for speech processing. Home page is at % 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<2 low=0.5; end if nargin<3 xmax=max(x); xmin=min(x); low=(xmax-xmin)*(1-low)/2; high=xmax-low; low=xmin+low; end c=(x>high)-(x<low); c(2:end)=c(2:end).*(c(2:end)~=c(1:end-1)); t=find(c); t(1+find(c(t(2:end))==c(t(1:end-1))))=[]; if nargout>1 y=c(t); else y=zeros(size(c)); if ~isempty(t) y(t)=2*c(t); y(t(1))=c(t(1)); y=cumsum(y); end end