| /* |
| * 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. |
| */ |
| |
| #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; |
| } |
| |
