1 /* 2 ** Copyright 2003-2010, VisualOn, Inc. 3 ** 4 ** Licensed under the Apache License, Version 2.0 (the "License"); 5 ** you may not use this file except in compliance with the License. 6 ** You may obtain a copy of the License at 7 ** 8 ** http://www.apache.org/licenses/LICENSE-2.0 9 ** 10 ** Unless required by applicable law or agreed to in writing, software 11 ** distributed under the License is distributed on an "AS IS" BASIS, 12 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 ** See the License for the specific language governing permissions and 14 ** limitations under the License. 15 */ 16 17 /*********************************************************************** 18 * File: hp50.c * 19 * * 20 * Description: * 21 * 2nd order high pass filter with cut off frequency at 31 Hz. * 22 * Designed with cheby2 function in MATLAB. * 23 * Optimized for fixed-point to get the following frequency response: * 24 * * 25 * frequency: 0Hz 14Hz 24Hz 31Hz 37Hz 41Hz 47Hz * 26 * dB loss: -infdB -15dB -6dB -3dB -1.5dB -1dB -0.5dB * 27 * * 28 * Algorithm: * 29 * * 30 * y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2] * 31 * + a[1]*y[i-1] + a[2]*y[i-2]; * 32 * * 33 * Word16 b[3] = {4053, -8106, 4053}; in Q12 * 34 * Word16 a[3] = {8192, 16211, -8021}; in Q12 * 35 * * 36 * float --> b[3] = {0.989501953, -1.979003906, 0.989501953}; * 37 * a[3] = {1.000000000, 1.978881836, -0.979125977}; * 38 ************************************************************************/ 39 40 #include "typedef.h" 41 #include "basic_op.h" 42 #include "oper_32b.h" 43 #include "cnst.h" 44 #include "acelp.h" 45 46 /* filter coefficients */ 47 static Word16 b[3] = {4053, -8106, 4053}; /* Q12 */ 48 static Word16 a[3] = {8192, 16211, -8021}; /* Q12 (x2) */ 49 50 /* Initialization of static values */ 51 52 void Init_HP50_12k8(Word16 mem[]) 53 { 54 Set_zero(mem, 6); 55 } 56 57 58 void HP50_12k8( 59 Word16 signal[], /* input/output signal */ 60 Word16 lg, /* lenght of signal */ 61 Word16 mem[] /* filter memory [6] */ 62 ) 63 { 64 Word16 x2; 65 Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1; 66 Word32 L_tmp; 67 Word32 num; 68 69 y2_hi = *mem++; 70 y2_lo = *mem++; 71 y1_hi = *mem++; 72 y1_lo = *mem++; 73 x0 = *mem++; 74 x1 = *mem; 75 num = (Word32)lg; 76 do 77 { 78 x2 = x1; 79 x1 = x0; 80 x0 = *signal; 81 /* y[i] = b[0]*x[i] + b[1]*x[i-1] + b140[2]*x[i-2] */ 82 /* + a[1]*y[i-1] + a[2] * y[i-2]; */ 83 L_tmp = 8192 ; /* rounding to maximise precision */ 84 L_tmp += y1_lo * a[1]; 85 L_tmp += y2_lo * a[2]; 86 L_tmp = L_tmp >> 14; 87 L_tmp += (y1_hi * a[1] + y2_hi * a[2] + (x0 + x2) * b[0] + x1 * b[1]) << 1; 88 L_tmp <<= 2; /* coeff Q12 --> Q13 */ 89 y2_hi = y1_hi; 90 y2_lo = y1_lo; 91 y1_hi = (Word16)(L_tmp>>16); 92 y1_lo = (Word16)((L_tmp & 0xffff)>>1); 93 *signal++ = extract_h((L_add((L_tmp<<1), 0x8000))); 94 }while(--num !=0); 95 96 *mem-- = x1; 97 *mem-- = x0; 98 *mem-- = y1_lo; 99 *mem-- = y1_hi; 100 *mem-- = y2_lo; 101 *mem-- = y2_hi; 102 103 return; 104 } 105 106 107
