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