/* * QCELP decoder * Copyright (c) 2007 Reynaldo H. Verdejo Pinochet * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /** * @file qcelp_lsp.c * QCELP decoder * @author Reynaldo H. Verdejo Pinochet * @remark FFmpeg merging spearheaded by Kenan Gillet * @remark Development mentored by Benjamin Larson */ #include "libavutil/mathematics.h" /** * initial coefficient to perform bandwidth expansion on LPC * * @note: 0.9883 looks like an approximation of 253/256. * * TIA/EIA/IS-733 2.4.3.3.6 6 */ #define QCELP_BANDWITH_EXPANSION_COEFF 0.9883 /** * Computes the Pa / (1 + z(-1)) or Qa / (1 - z(-1)) coefficients * needed for LSP to LPC conversion. * We only need to calculate the 6 first elements of the polynomial. * * @param lspf line spectral pair frequencies * @param f [out] polynomial input/output as a vector * * TIA/EIA/IS-733 2.4.3.3.5-1/2 */ static void lsp2polyf(const float *lspf, double *f, int lp_half_order) { int i, j; f[0] = 1.0; f[1] = -2 * cos(M_PI * lspf[0]); lspf -= 2; for(i=2; i<=lp_half_order; i++) { double val = -2 * cos(M_PI * lspf[2*i]); f[i] = val * f[i-1] + 2*f[i-2]; for(j=i-1; j>1; j--) f[j] += f[j-1] * val + f[j-2]; f[1] += val; } } /** * Reconstructs LPC coefficients from the line spectral pair frequencies * and performs bandwidth expansion. * * @param lspf line spectral pair frequencies * @param lpc linear predictive coding coefficients * * @note: bandwith_expansion_coeff could be precalculated into a table * but it seems to be slower on x86 * * TIA/EIA/IS-733 2.4.3.3.5 */ void ff_qcelp_lspf2lpc(const float *lspf, float *lpc) { double pa[6], qa[6]; int i; double bandwith_expansion_coeff = -QCELP_BANDWITH_EXPANSION_COEFF * 0.5; lsp2polyf(lspf, pa, 5); lsp2polyf(lspf + 1, qa, 5); for (i=4; i>=0; i--) { double paf = pa[i+1] + pa[i]; double qaf = qa[i+1] - qa[i]; lpc[i ] = paf + qaf; lpc[9-i] = paf - qaf; } for (i=0; i<10; i++) { lpc[i] *= bandwith_expansion_coeff; bandwith_expansion_coeff *= QCELP_BANDWITH_EXPANSION_COEFF; } }