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 "LVC_Mixer_Private.h" 21 22 /************************************************************************/ 23 /* FUNCTION: */ 24 /* LVMixer3_SetTimeConstant */ 25 /* */ 26 /* DESCRIPTION: */ 27 /* This function calculates the step change for fractional gain for a */ 28 /* given time constant, sample rate and num channels */ 29 /* Delta=(2147483647*4*1000)/(NumChannels*SampleRate*Tc_millisec) */ 30 /* in Q 0.31 format */ 31 /* */ 32 /* PARAMETERS: */ 33 /* pStream - ptr to Instance Parameter Structure LVMixer3_st for an*/ 34 /* Audio Stream */ 35 /* Tc_millisec - TimeConstant i.e time required in milli second to */ 36 /* go from linear fractional gain of 0 to 0.99999999 */ 37 /* Fs - LVM_Fs_en enumerator for Sampling Frequency */ 38 /* NumChannels - Number of channels in Audio Stream 1=Mono, 2=Stereo */ 39 /* */ 40 /* UPDATES: */ 41 /* Delta - the step change for fractional gain per 4 samples */ 42 /* in Q0.31 format for a given Time Constant, */ 43 /* Sample Rate and NumChannels */ 44 /* RETURNS: */ 45 /* void */ 46 /************************************************************************/ 47 48 void LVC_Mixer_SetTimeConstant(LVMixer3_st *pStream, 49 LVM_INT32 Tc_millisec, 50 LVM_Fs_en Fs, 51 LVM_INT16 NumChannels) 52 { 53 LVM_INT32 DeltaTable[9]={1073741824, 54 779132389, 55 715827882, 56 536870912, 57 389566194, 58 357913941, 59 268435456, 60 194783097, 61 178956971}; 62 Mix_Private_st *pInstance=(Mix_Private_st *)pStream->PrivateParams; 63 LVM_INT32 Delta=DeltaTable[Fs]; 64 Delta=Delta>>(NumChannels-1); 65 66 if(Tc_millisec==0) 67 Delta=0x7FFFFFFF; 68 else 69 Delta=Delta/Tc_millisec; 70 71 if(Delta==0) 72 Delta=1; // If Time Constant is so large that Delta is 0, assign minimum value to Delta 73 74 pInstance->Delta=Delta; // Delta=(2147483647*4*1000)/(NumChannels*SampleRate*Tc_millisec) in Q 0.31 format 75 } 76
