1/* 2 * QCELP decoder 3 * Copyright (c) 2007 Reynaldo H. Verdejo Pinochet 4 * 5 * This file is part of FFmpeg. 6 * 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. 11 * 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. 16 * 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 20 */ 21 22/** 23 * @file libavcodec/qcelp_lsp.c 24 * QCELP decoder 25 * @author Reynaldo H. Verdejo Pinochet 26 * @remark FFmpeg merging spearheaded by Kenan Gillet 27 * @remark Development mentored by Benjamin Larson 28 */ 29 30#include "libavutil/mathematics.h" 31 32/** 33 * initial coefficient to perform bandwidth expansion on LPC 34 * 35 * @note: 0.9883 looks like an approximation of 253/256. 36 * 37 * TIA/EIA/IS-733 2.4.3.3.6 6 38 */ 39#define QCELP_BANDWITH_EXPANSION_COEFF 0.9883 40 41/** 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. 45 * 46 * @param lspf line spectral pair frequencies 47 * @param f [out] polynomial input/output as a vector 48 * 49 * TIA/EIA/IS-733 2.4.3.3.5-1/2 50 */ 51static void lsp2polyf(const float *lspf, double *f, int lp_half_order) 52{ 53 int i, j; 54 55 f[0] = 1.0; 56 f[1] = -2 * cos(M_PI * lspf[0]); 57 lspf -= 2; 58 for(i=2; i<=lp_half_order; i++) 59 { 60 double val = -2 * cos(M_PI * lspf[2*i]); 61 f[i] = val * f[i-1] + 2*f[i-2]; 62 for(j=i-1; j>1; j--) 63 f[j] += f[j-1] * val + f[j-2]; 64 f[1] += val; 65 } 66} 67 68/** 69 * Reconstructs LPC coefficients from the line spectral pair frequencies 70 * and performs bandwidth expansion. 71 * 72 * @param lspf line spectral pair frequencies 73 * @param lpc linear predictive coding coefficients 74 * 75 * @note: bandwith_expansion_coeff could be precalculated into a table 76 * but it seems to be slower on x86 77 * 78 * TIA/EIA/IS-733 2.4.3.3.5 79 */ 80void ff_qcelp_lspf2lpc(const float *lspf, float *lpc) 81{ 82 double pa[6], qa[6]; 83 int i; 84 double bandwith_expansion_coeff = QCELP_BANDWITH_EXPANSION_COEFF * 0.5; 85 86 lsp2polyf(lspf, pa, 5); 87 lsp2polyf(lspf + 1, qa, 5); 88 89 for (i=4; i>=0; i--) 90 { 91 double paf = pa[i+1] + pa[i]; 92 double qaf = qa[i+1] - qa[i]; 93 94 lpc[i ] = paf + qaf; 95 lpc[9-i] = paf - qaf; 96 } 97 for (i=0; i<10; i++) 98 { 99 lpc[i] *= bandwith_expansion_coeff; 100 bandwith_expansion_coeff *= QCELP_BANDWITH_EXPANSION_COEFF; 101 } 102} 103