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Diffstat (limited to 'media/libeffects/lvm/lib/Common/src/LVM_FO_LPF.c')
| -rwxr-xr-x | media/libeffects/lvm/lib/Common/src/LVM_FO_LPF.c | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/media/libeffects/lvm/lib/Common/src/LVM_FO_LPF.c b/media/libeffects/lvm/lib/Common/src/LVM_FO_LPF.c new file mode 100755 index 0000000..6c73d59 --- /dev/null +++ b/media/libeffects/lvm/lib/Common/src/LVM_FO_LPF.c @@ -0,0 +1,106 @@ +/* + * Copyright (C) 2004-2010 NXP Software + * Copyright (C) 2010 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +/************************************************************************/ +/* */ +/* Project:: */ +/* $Author: nxp27078 $*/ +/* $Revision: 762 $*/ +/* $Date: 2010-06-11 14:50:33 +0200 (vr, 11 jun 2010) $*/ +/* */ +/************************************************************************/ + +#include "LVM_Types.h" +#include "LVM_Macros.h" +#include "ScalarArithmetic.h" +#include "BIQUAD.h" +#include "Filter.h" + + +/*-------------------------------------------------------------------------*/ +/* FUNCTION: */ +/* void LVM_FO_LPF( LVM_INT32 w , */ +/* FO_C32_Coefs_t *pCoeffs); */ +/* */ +/* */ +/* DESCRIPTION: */ +/* This function calculates the coefficient of first order low pass */ +/* filter. It uses the equations: */ +/* */ +/* B1 = (tan(w/2) - 1 ) / (tan(w/2) + 1 ) */ +/* A0 = (1 + B1) / 2 */ +/* A1 = A0 */ +/* */ +/* The value of B1 is then calculated directly from the value w by a */ +/* polynomial expansion using a 9th order polynomial. It uses the */ +/* following table of 32-bit integer polynomial coefficients: */ +/* */ +/* Coefficient Value */ +/* A0 -8388571 */ +/* A1 33547744 */ +/* A2 -66816791 */ +/* A3 173375308 */ +/* A4 -388437573 */ +/* A5 752975383 */ +/* A6 -1103016663 */ +/* A7 1121848567 */ +/* A8 -688078159 */ +/* A9 194669577 */ +/* A10 8 */ +/* */ +/* Y = (A0 + A1*X + A2*X2 + A3*X3 + ….. + AN*xN) << AN+1 */ +/* */ +/* */ +/* PARAMETERS: */ +/* */ +/* w Sample rate in radians, where: */ +/* w = 2 * Pi * Fc / Fs */ +/* Fc is the corner frequency in Hz */ +/* Fs is the sample rate in Hz */ +/* w is in Q2.29 format and data range is [0 Pi] */ +/* pCoeffs Points to the filter coefficients calculated here */ +/* in Q1.30 format */ +/* RETURNS: */ +/* */ +/*-------------------------------------------------------------------------*/ + +LVM_INT32 LVM_FO_LPF( LVM_INT32 w, + FO_C32_Coefs_t *pCoeffs) +{ + LVM_INT32 Y,Coefficients[13]={ -8388571, + 33547744, + -66816791, + 173375308, + -388437573, + 752975383, + -1103016663, + 1121848567, + -688078159, + 194669577, + 8}; + Y=LVM_Polynomial( (LVM_UINT16)9, + Coefficients, + w); + pCoeffs->B1=-Y; // Store -B1 in filter structure instead of B1! + // A0=(1+B1)/2= B1/2 + 0.5 + Y=Y>>1; // A0=Y=B1/2 + Y=Y+0x40000000; // A0=Y=(B1/2 + 0.5) + MUL32x16INTO32(Y, FILTER_LOSS ,pCoeffs->A0 ,15) // Apply loss to avoid overflow + pCoeffs->A1=pCoeffs->A0; + return 1; +} + |