/usr/share/octave/packages/signal-1.3.2/chirp.m is in octave-signal 1.3.2-1+b1.
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 | ## Copyright (C) 1999-2000 Paul Kienzle <pkienzle@users.sf.net>
##
## 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} {} chirp (@var{t})
## @deftypefnx {Function File} {} chirp (@var{t}, @var{f0})
## @deftypefnx {Function File} {} chirp (@var{t}, @var{f0}, @var{t1})
## @deftypefnx {Function File} {} chirp (@var{t}, @var{f0}, @var{t1}, @var{f1})
## @deftypefnx {Function File} {} chirp (@var{t}, @var{f0}, @var{t1}, @var{f1}, @var{form})
## @deftypefnx {Function File} {} chirp (@var{t}, @var{f0}, @var{t1}, @var{f1}, @var{form}, @var{phase})
##
## Evaluate a chirp signal at time @var{t}. A chirp signal is a frequency
## swept cosine wave.
##
## @table @var
## @item t
## vector of times to evaluate the chirp signal
## @item f0
## frequency at time t=0 [ 0 Hz ]
## @item t1
## time t1 [ 1 sec ]
## @item f1
## frequency at time t=t1 [ 100 Hz ]
## @item form
## shape of frequency sweep
## 'linear' f(t) = (f1-f0)*(t/t1) + f0
## 'quadratic' f(t) = (f1-f0)*(t/t1)^2 + f0
## 'logarithmic' f(t) = (f1-f0)^(t/t1) + f0
## @item phase
## phase shift at t=0
## @end table
##
## Example
## specgram(chirp([0:0.001:5])); # linear, 0-100Hz in 1 sec
## specgram(chirp([-2:0.001:15], 400, 10, 100, 'quadratic'));
## soundsc(chirp([0:1/8000:5], 200, 2, 500, "logarithmic"),8000);
##
## If you want a different sweep shape f(t), use the following:
## y = cos(2*pi*integral(f(t)) + 2*pi*f0*t + phase);
## @end deftypefn
function y = chirp(t, f0, t1, f1, form, phase)
if nargin < 1 || nargin > 6
print_usage;
endif
if nargin < 2, f0 = []; endif
if nargin < 3, t1 = []; endif
if nargin < 4, f1 = []; endif
if nargin < 5, form = []; endif
if nargin < 6, phase = []; endif
if isempty(f0), f0 = 0; endif
if isempty(t1), t1 = 1; endif
if isempty(f1), f1 = 100; endif
if isempty(form), form = "linear"; endif
if isempty(phase), phase = 0; endif
phase = 2*pi*phase/360;
if strcmp(form, "linear")
a = pi*(f1 - f0)/t1;
b = 2*pi*f0;
y = cos(a*t.^2 + b*t + phase);
elseif strcmp(form, "quadratic")
a = (2/3*pi*(f1-f0)/t1/t1);
b = 2*pi*f0;
y = cos(a*t.^3 + b*t + phase);
elseif strcmp(form, "logarithmic")
a = 2*pi*t1/log(f1-f0);
b = 2*pi*f0;
x = (f1-f0)^(1/t1);
y = cos(a*x.^t + b*t + phase);
else
error("chirp doesn't understand '%s'",form);
endif
endfunction
%!demo
%! specgram(chirp([0:0.001:5]), 256, 1000); # linear, 0-100Hz in 1 sec
%! %------------------------------------------------------------
%! % Shows linear sweep of 100 Hz/sec starting at zero for 5 sec
%! % since the sample rate is 1000 Hz, this should be a diagonal
%! % from bottom left to top right.
%!demo
%! specgram(chirp([-2:0.001:15], 400, 10, 100, 'quadratic'));
%! %------------------------------------------------------------
%! % Shows a quadratic chirp of 400 Hz at t=0 and 100 Hz at t=10
%! % Time goes from -2 to 15 seconds.
%!demo
%! specgram(chirp([0:1/8000:5], 200, 2, 500, "logarithmic"), 256, 8000);
%! %------------------------------------------------------------
%! % Shows a logarithmic chirp of 200 Hz at t=0 and 500 Hz at t=2
%! % Time goes from 0 to 5 seconds at 8000 Hz.
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