/usr/share/octave/packages/communications-1.1.1/compand.m is in octave-communications-common 1.1.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 | ## 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
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