Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / communications-1.1.1 / compand.m

diff --git a/octave_packages/communications-1.1.1/compand.m b/octave_packages/communications-1.1.1/compand.m
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+## Copyright (C) 2001 Paul Kienzle
+##
+## 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 3 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 should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{y} = } compand (@var{x}, @var{mu}, @var{V}, 'mu/compressor')
+## @deftypefnx {Function File} {@var{y} = } compand (@var{x}, @var{mu}, @var{V}, 'mu/expander')
+## @deftypefnx {Function File} {@var{y} = } compand (@var{x}, @var{mu}, @var{V}, 'A/compressor')
+## @deftypefnx {Function File} {@var{y} = } compand (@var{x}, @var{mu}, @var{V}, 'A/expander')
+##
+## Compresses and expanding the dynamic range of a signal using a mu-law or
+## or A-law algorithm.
+##
+## The mu-law compressor/expander for reducing the dynamic range, is used
+## if the fourth argument of @dfn{compand} starts with 'mu/'. Whereas the
+## A-law compressor/expander is used if @dfn{compand} starts with 'A/'.
+## The mu-law algorithm uses the formulation
+##
+## @iftex
+## @tex
+## $$
+## y = {V log (1 + \\mu / V \\|x\\|) \\over log (1 + \\mu)} sgn(x)
+## $$
+## @end tex
+## @end iftex
+## @ifinfo
+## @example
+##
+##         V log (1 + \mu/V |x|)
+##     y = -------------------- sgn(x)
+##             log (1 + \mu)
+##
+## @end example
+## @end ifinfo
+##
+## while the A-law algorithm used the formulation
+##
+## @iftex
+## @tex
+## $$
+## y = { \\left\{  \\matrix{ {A / (1 + log A) x}, & 0 <= \\|x\\| <= V/A \\cr
+##                  & \\cr  
+##                  {V log (1 + log(A/V \\|x\\|) ) \\over 1 + logA}, &
+##                  V/A < \\|x\\| <= V} \\right. }
+## $$
+## @end tex
+## @end iftex
+## @ifinfo
+## @example
+##
+##         /    A / (1 + log A) x,               0 <= |x| <= V/A  
+##         | 
+##     y = <    V ( 1 + log (A/V |x|) )
+##         |    ----------------------- sgn(x),  V/A < |x| <= V
+##         \        1 + log A
+## @end example
+## @end ifinfo
+##
+## Neither converts from or to audio file ulaw format. Use mu2lin or lin2mu
+## instead.
+##
+## @end deftypefn
+## @seealso{m2ulin, lin2mu}
+
+function y = compand(x, mu, V, stype)
+
+  if (nargin != 3 && nargin != 4)
+    usage('y=compand(x,[mu|A],V,stype);'); 
+  endif
+  if (nargin < 4) 
+    stype = 'mu/compressor';
+  else 
+    stype = tolower(stype);
+  endif
+
+  if strcmp(stype, 'mu/compressor')
+    y = (V/log(1+mu)) * log(1+(mu/V)*abs(x)) .* sign(x);
+  elseif strcmp(stype, 'mu/expander')
+    y = (V/mu) * ( exp (abs(x) * (log(1+mu)/V)) - 1 ) .* sign(x);
+  elseif strcmp(stype, 'a/compressor')
+    y = zeros(size(x));
+    idx = find (abs(x) <= V/mu);
+    if (idx)
+      y(idx) = (mu/(1+log(mu))) * abs(x(idx));
+    endif
+    idx = find (abs(x) > V/mu);
+    if (idx)
+      y(idx) = (V/(1+log(mu))) * (1 + log ((mu/V) * abs(x(idx))));
+    endif
+    y = y .* sign(x);
+  elseif strcmp(stype, 'a/expander')
+    y = zeros(size(x));
+    idx = find (abs(x) <= V/(1+log(mu)));
+    if (idx)
+      y(idx) = ((1+log(mu))/mu) * abs(x(idx));
+    endif
+    idx = find (abs(x) > V/(1+log(mu)));
+    if (idx)
+      y(idx) = exp (((1+log(mu))/V) * abs(x(idx)) - 1) * (V/mu);
+    endif
+    y = y .* sign(x);
+  endif
+
+endfunction
+