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1 ## Copyright (C) 1999-2000 Paul Kienzle |
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2 ## |
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3 ## This program is free software; you can redistribute it and/or modify |
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4 ## it under the terms of the GNU General Public License as published by |
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5 ## the Free Software Foundation; either version 2 of the License, or |
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6 ## (at your option) any later version. |
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7 ## |
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8 ## This program is distributed in the hope that it will be useful, |
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9 ## but WITHOUT ANY WARRANTY; without even the implied warranty of |
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10 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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11 ## GNU General Public License for more details. |
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12 ## |
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13 ## You should have received a copy of the GNU General Public License |
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14 ## along with this program; if not, write to the Free Software |
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15 ## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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16 |
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17 ## usage: y = chirp(t [, f0 [, t1 [, f1 [, form [, phase]]]]]) |
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18 ## |
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19 ## Evaluate a chirp signal at time t. A chirp signal is a frequency |
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20 ## swept cosine wave. |
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21 ## |
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22 ## t: vector of times to evaluate the chirp signal |
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23 ## f0: frequency at time t=0 [ 0 Hz ] |
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24 ## t1: time t1 [ 1 sec ] |
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25 ## f1: frequency at time t=t1 [ 100 Hz ] |
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26 ## form: shape of frequency sweep |
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27 ## 'linear' f(t) = (f1-f0)*(t/t1) + f0 |
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28 ## 'quadratic' f(t) = (f1-f0)*(t/t1)^2 + f0 |
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29 ## 'logarithmic' f(t) = (f1-f0)^(t/t1) + f0 |
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30 ## phase: phase shift at t=0 |
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31 ## |
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32 ## Example |
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33 ## specgram(chirp([0:0.001:5])); # linear, 0-100Hz in 1 sec |
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34 ## specgram(chirp([-2:0.001:15], 400, 10, 100, 'quadratic')); |
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35 ## soundsc(chirp([0:1/8000:5], 200, 2, 500, "logarithmic"),8000); |
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36 ## |
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37 ## If you want a different sweep shape f(t), use the following: |
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38 ## y = cos(2*pi*integral(f(t)) + 2*pi*f0*t + phase); |
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39 |
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40 ## 2001-08-31 Paul Kienzle <pkienzle@users.sf.net> |
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41 ## * Fix documentation for quadratic case |
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42 |
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43 function y = chirp(t, f0, t1, f1, form, phase) |
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44 |
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45 if nargin < 1 || nargin > 6 |
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46 usage("y = chirp(t [, f0 [, t1 [, f1 [, form [, phase]]]]])"); |
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47 endif |
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48 if nargin < 2, f0 = []; endif |
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49 if nargin < 3, t1 = []; endif |
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50 if nargin < 4, f1 = []; endif |
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51 if nargin < 5, form = []; endif |
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52 if nargin < 6, phase = []; endif |
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53 |
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54 if isempty(f0), f0 = 0; endif |
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55 if isempty(t1), t1 = 1; endif |
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56 if isempty(f1), f1 = 100; endif |
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57 if isempty(form), form = "linear"; endif |
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58 if isempty(phase), phase = 0; endif |
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59 |
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60 phase = 2*pi*phase/360; |
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61 |
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62 if strcmp(form, "linear") |
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63 a = pi*(f1 - f0)/t1; |
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64 b = 2*pi*f0; |
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65 y = cos(a*t.^2 + b*t + phase); |
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66 elseif strcmp(form, "quadratic") |
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67 a = (2/3*pi*(f1-f0)/t1/t1); |
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68 b = 2*pi*f0; |
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69 y = cos(a*t.^3 + b*t + phase); |
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70 elseif strcmp(form, "logarithmic") |
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71 a = 2*pi*t1/log(f1-f0); |
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72 b = 2*pi*f0; |
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73 x = (f1-f0)^(1/t1); |
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74 y = cos(a*x.^t + b*t + phase); |
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75 else |
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76 error("chirp doesn't understand '%s'",form); |
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77 endif |
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78 |
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79 endfunction |
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80 |
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81 %!demo |
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82 %! specgram(chirp([0:0.001:5]),[],1000); # linear, 0-100Hz in 1 sec |
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83 %! %------------------------------------------------------------ |
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84 %! % Shows linear sweep of 100 Hz/sec starting at zero for 5 sec |
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85 %! % since the sample rate is 1000 Hz, this should be a diagonal |
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86 %! % from bottom left to top right. |
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87 |
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88 %!demo |
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89 %! specgram(chirp([-2:0.001:15], 400, 10, 100, 'quadratic')); |
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90 %! %------------------------------------------------------------ |
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91 %! % Shows a quadratic chirp of 400 Hz at t=0 and 100 Hz at t=10 |
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92 %! % Time goes from -2 to 15 seconds. |
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93 |
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94 %!demo |
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95 %! specgram(chirp([0:1/8000:5], 200, 2, 500, "logarithmic"),[],8000); |
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96 %! %------------------------------------------------------------ |
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97 %! % Shows a logarithmic chirp of 200 Hz at t=0 and 500 Hz at t=2 |
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98 %! % Time goes from 0 to 5 seconds at 8000 Hz. |
