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120 lines
4.1 KiB
120 lines
4.1 KiB
14 years ago
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/*
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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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