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
23 * @file libavcodec/qcelp_lsp.c
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 * Computes the Pa / (1 + z(-1)) or Qa / (1 - z(-1)) coefficients
34 * needed for LSP to LPC conversion.
35 * We only need to calculate the 6 first elements of the polynomial.
37 * @param lspf line spectral pair frequencies
38 * @param f [out] polynomial input/output as a vector
40 * TIA/EIA/IS-733 2.4.3.3.5-1/2
42 static void lsp2polyf(const double *lspf
, double *f
, int lp_half_order
)
49 for(i
=2; i
<=lp_half_order
; i
++)
51 double val
= -2 * lspf
[2*i
];
52 f
[i
] = val
* f
[i
-1] + 2*f
[i
-2];
54 f
[j
] += f
[j
-1] * val
+ f
[j
-2];
60 * Reconstructs LPC coefficients from the line spectral pair frequencies.
62 * @param lspf line spectral pair frequencies
63 * @param lpc linear predictive coding coefficients
65 void ff_celp_lspf2lpc(const double *lspf
, float *lpc
)
70 lsp2polyf(lspf
, pa
, 5);
71 lsp2polyf(lspf
+ 1, qa
, 5);
75 double paf
= pa
[i
+1] + pa
[i
];
76 double qaf
= qa
[i
+1] - qa
[i
];
78 lpc
[i
] = 0.5*(paf
+qaf
);
79 lpc
[9-i
] = 0.5*(paf
-qaf
);