From b237248e297760648307356efa5fcbfe16844829 Mon Sep 17 00:00:00 2001 From: Justin Ruggles Date: Sun, 20 Nov 2011 14:21:32 -0500 Subject: adx: calculate correct LPC coeffs Instead of using fixed coefficients, the correct way is to calculate the coefficients using the highpass cutoff frequency from the ADX stream header and the sample rate. --- libavcodec/adx.c | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) create mode 100644 libavcodec/adx.c (limited to 'libavcodec/adx.c') diff --git a/libavcodec/adx.c b/libavcodec/adx.c new file mode 100644 index 0000000000..bc3e8825ca --- /dev/null +++ b/libavcodec/adx.c @@ -0,0 +1,34 @@ +/* + * Copyright (c) 2011 Justin Ruggles + * + * This file is part of Libav. + * + * Libav 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. + * + * Libav 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 Libav; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#include "libavutil/mathematics.h" +#include "adx.h" + +void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff) +{ + double a, b, c; + + a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate); + b = M_SQRT2 - 1.0; + c = (a - sqrt((a + b) * (a - b))) / b; + + coeff[0] = lrintf(c * 2.0 * (1 << bits)); + coeff[1] = lrintf(-(c * c) * (1 << bits)); +} -- cgit v1.2.3