1 /* 2 * Copyright (C) 2004-2010 NXP Software 3 * Copyright (C) 2010 The Android Open Source Project 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 #include "LVM_Types.h" 19 #include "LVM_Macros.h" 20 #include "ScalarArithmetic.h" 21 #include "BIQUAD.h" 22 #include "Filter.h" 23 24 25 /*-------------------------------------------------------------------------*/ 26 /* FUNCTION: */ 27 /* void LVM_FO_LPF( LVM_INT32 w , */ 28 /* FO_C32_Coefs_t *pCoeffs); */ 29 /* */ 30 /* */ 31 /* DESCRIPTION: */ 32 /* This function calculates the coefficient of first order low pass */ 33 /* filter. It uses the equations: */ 34 /* */ 35 /* B1 = (tan(w/2) - 1 ) / (tan(w/2) + 1 ) */ 36 /* A0 = (1 - B1) / 2 */ 37 /* A1 = A0 */ 38 /* */ 39 /* The value of B1 is then calculated directly from the value w by a */ 40 /* polynomial expansion using a 9th order polynomial. It uses the */ 41 /* following table of 32-bit integer polynomial coefficients: */ 42 /* */ 43 /* Coefficient Value */ 44 /* A0 -8388571 */ 45 /* A1 33547744 */ 46 /* A2 -66816791 */ 47 /* A3 173375308 */ 48 /* A4 -388437573 */ 49 /* A5 752975383 */ 50 /* A6 -1103016663 */ 51 /* A7 1121848567 */ 52 /* A8 -688078159 */ 53 /* A9 194669577 */ 54 /* A10 8 */ 55 /* */ 56 /* Y = (A0 + A1*X + A2*X2 + A3*X3 + .. + AN*xN) << AN+1 */ 57 /* */ 58 /* */ 59 /* PARAMETERS: */ 60 /* */ 61 /* w Sample rate in radians, where: */ 62 /* w = 2 * Pi * Fc / Fs */ 63 /* Fc is the corner frequency in Hz */ 64 /* Fs is the sample rate in Hz */ 65 /* w is in Q2.29 format and data range is [0 Pi] */ 66 /* pCoeffs Points to the filter coefficients calculated here */ 67 /* in Q1.30 format */ 68 /* RETURNS: */ 69 /* */ 70 /*-------------------------------------------------------------------------*/ 71 72 LVM_INT32 LVM_FO_HPF( LVM_INT32 w, 73 FO_C32_Coefs_t *pCoeffs) 74 { 75 LVM_INT32 Y,Coefficients[13]={ -8388571, 76 33547744, 77 -66816791, 78 173375308, 79 -388437573, 80 752975383, 81 -1103016663, 82 1121848567, 83 -688078159, 84 194669577, 85 8, 86 0, 87 0}; 88 Y=LVM_Polynomial( (LVM_UINT16)9, 89 Coefficients, 90 w); 91 pCoeffs->B1=-Y; /* Store -B1 in filter structure instead of B1!*/ 92 /* A0=(1-B1)/2= B1/2 - 0.5*/ 93 Y=Y>>1; /* A0=Y=B1/2*/ 94 Y=Y-0x40000000; /* A0=Y=(B1/2 - 0.5)*/ 95 MUL32x16INTO32(Y, FILTER_LOSS ,pCoeffs->A0 ,15) /* Apply loss to avoid overflow*/ 96 pCoeffs->A1=-pCoeffs->A0; /* Store A1=-A0*/ 97 98 return 1; 99 } 100 101
