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119 lines
3.9 KiB
119 lines
3.9 KiB
/* |
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Copyright 1992, 1993, 1994 by Jutta Degener and Carsten Bormann, |
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Technische Universitaet Berlin |
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Any use of this software is permitted provided that this notice is not |
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removed and that neither the authors nor the Technische Universitaet Berlin |
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are deemed to have made any representations as to the suitability of this |
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software for any purpose nor are held responsible for any defects of |
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this software. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE. |
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As a matter of courtesy, the authors request to be informed about uses |
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this software has found, about bugs in this software, and about any |
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improvements that may be of general interest. |
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Berlin, 28.11.1994 |
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Jutta Degener |
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Carsten Bormann |
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Code slightly modified by Jean-Marc Valin |
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Speex License: |
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Redistribution and use in source and binary forms, with or without |
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modification, are permitted provided that the following conditions |
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are met: |
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- Redistributions of source code must retain the above copyright |
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notice, this list of conditions and the following disclaimer. |
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- Redistributions in binary form must reproduce the above copyright |
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notice, this list of conditions and the following disclaimer in the |
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documentation and/or other materials provided with the distribution. |
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- Neither the name of the Xiph.org Foundation nor the names of its |
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contributors may be used to endorse or promote products derived from |
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this software without specific prior written permission. |
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
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``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR |
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CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
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PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF |
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING |
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NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS |
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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*/ |
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/* LPC- and Reflection Coefficients |
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* |
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* The next two functions calculate linear prediction coefficients |
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* and/or the related reflection coefficients from the first P_MAX+1 |
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* values of the autocorrelation function. |
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*/ |
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/* Invented by N. Levinson in 1947, modified by J. Durbin in 1959. |
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*/ |
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#include "lpc.h" |
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float /* returns minimum mean square error */ |
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wld( |
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float * lpc, /* [0...p-1] LPC coefficients */ |
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const float * ac, /* in: [0...p] autocorrelation values */ |
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float * ref, /* out: [0...p-1] reflection coef's */ |
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int p |
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) |
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{ |
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int i, j; float r, error = ac[0]; |
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if (ac[0] == 0) { |
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for (i = 0; i < p; i++) ref[i] = 0; return 0; } |
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for (i = 0; i < p; i++) { |
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/* Sum up this iteration's reflection coefficient. |
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*/ |
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r = -ac[i + 1]; |
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for (j = 0; j < i; j++) r -= lpc[j] * ac[i - j]; |
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ref[i] = r /= error; |
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/* Update LPC coefficients and total error. |
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*/ |
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lpc[i] = r; |
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for (j = 0; j < i/2; j++) { |
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float tmp = lpc[j]; |
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lpc[j] += r * lpc[i-1-j]; |
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lpc[i-1-j] += r * tmp; |
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} |
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if (i % 2) lpc[j] += lpc[j] * r; |
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error *= 1.0 - r * r; |
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} |
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return error; |
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} |
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/* Compute the autocorrelation |
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* ,--, |
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* ac(i) = > x(n) * x(n-i) for all n |
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* `--' |
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* for lags between 0 and lag-1, and x == 0 outside 0...n-1 |
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*/ |
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void _spx_autocorr( |
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const float * x, /* in: [0...n-1] samples x */ |
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float *ac, /* out: [0...lag-1] ac values */ |
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int lag, int n) |
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{ |
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float d; int i; |
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while (lag--) { |
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for (i = lag, d = 0; i < n; i++) d += x[i] * x[i-lag]; |
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ac[lag] = d; |
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} |
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}
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