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1 ## Copyright (C) 1994 Dept of Probability Theory and Statistics TU Wien |
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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: cceps (x [, correct]) |
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18 ## |
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19 ## Returns the complex cepstrum of the vector x. |
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20 ## If the optional argument correct has the value 1, a correction |
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21 ## method is applied. The default is not to do this. |
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22 |
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23 ## Author: AW (Andreas.Weingessel@ci.tuwien.ac.at) on Apr 1, 1994 |
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24 ## Last modifified by AW on Nov 8, 1994 |
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25 |
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26 function cep = cceps (x, c) |
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27 |
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28 if (nargin == 1) |
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29 c = 0; |
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30 elseif (nargin != 2) |
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31 error ("usage: cceps (x [, correct])"); |
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32 endif |
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33 |
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34 [nr, nc] = size (x); |
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35 if (nc != 1) |
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36 if (nr == 1) |
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37 x = x'; |
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38 nr = nc; |
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39 else |
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40 error ("cceps: x must be a vector"); |
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41 endif |
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42 endif |
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43 |
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44 bad_signal_message = ["cceps: bad signal x, ", ... |
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45 "some Fourier coefficients are zero."]; |
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46 |
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47 F = fft (x); |
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48 if (min (abs (F)) == 0) |
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49 error (bad_signal_message); |
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50 endif |
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51 |
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52 # determine if correction necessary |
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53 half = fix (nr / 2); |
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54 cor = 0; |
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55 if (2 * half == nr) |
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56 cor = (c && (real (F (half + 1)) < 0)); |
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57 if (cor) |
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58 F = fft (x(1:nr-1)) |
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59 if (min (abs (F)) == 0) |
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60 error (bad_signal_message); |
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61 endif |
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62 endif |
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63 endif |
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64 |
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65 cep = fftshift (ifft (log (F))); |
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66 |
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67 # make result real |
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68 if (c) |
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69 cep = real (cep); |
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70 if (cor) |
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71 # make cepstrum of same length as input vector |
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72 cep (nr) = 0; |
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73 endif |
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74 endif |
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75 |
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76 endfunction |
