3 * Copyright (c) 2007 Reynaldo H. Verdejo Pinochet
5 * This file is part of FFmpeg.
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
25 * @author Reynaldo H. Verdejo Pinochet
26 * @remark FFmpeg merging spearheaded by Kenan Gillet
27 * @remark Development mentored by Benjamin Larson
30 #include "libavutil/mathematics.h"
33 * initial coefficient to perform bandwidth expansion on LPC
35 * @note: 0.9883 looks like an approximation of 253/256.
37 * TIA/EIA/IS-733 2.4.3.3.6 6
39 #define QCELP_BANDWITH_EXPANSION_COEFF 0.9883
42 * Computes the Pa / (1 + z(-1)) or Qa / (1 - z(-1)) coefficients
43 * needed for LSP to LPC conversion.
44 * We only need to calculate the 6 first elements of the polynomial.
46 * @param lspf line spectral pair frequencies
47 * @param f [out] polynomial input/output as a vector
49 * TIA/EIA/IS-733 2.4.3.3.5-1/2
51 static void lsp2polyf(const float *lspf, double *f, int lp_half_order)
56 f[1] = -2 * cos(M_PI * lspf[0]);
58 for(i=2; i<=lp_half_order; i++)
60 double val = -2 * cos(M_PI * lspf[2*i]);
61 f[i] = val * f[i-1] + 2*f[i-2];
63 f[j] += f[j-1] * val + f[j-2];
69 * Reconstructs LPC coefficients from the line spectral pair frequencies
70 * and performs bandwidth expansion.
72 * @param lspf line spectral pair frequencies
73 * @param lpc linear predictive coding coefficients
75 * @note: bandwith_expansion_coeff could be precalculated into a table
76 * but it seems to be slower on x86
78 * TIA/EIA/IS-733 2.4.3.3.5
80 void ff_qcelp_lspf2lpc(const float *lspf, float *lpc)
84 double bandwith_expansion_coeff = -QCELP_BANDWITH_EXPANSION_COEFF * 0.5;
86 lsp2polyf(lspf, pa, 5);
87 lsp2polyf(lspf + 1, qa, 5);
91 double paf = pa[i+1] + pa[i];
92 double qaf = qa[i+1] - qa[i];
99 lpc[i] *= bandwith_expansion_coeff;
100 bandwith_expansion_coeff *= QCELP_BANDWITH_EXPANSION_COEFF;