Alc/alcEcho.c

   1 /**
   2  * OpenAL cross platform audio library
   3  * Copyright (C) 2009 by Chris Robinson.
   4  * This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU Library General Public
   6  *  License as published by the Free Software Foundation; either
   7  *  version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  *  Library General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Library General Public
  15  *  License along with this library; if not, write to the
  16  *  Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17  *  Boston, MA  02111-1307, USA.
  18  * Or go to http://www.gnu.org/copyleft/lgpl.html
  19  */
  20
  21 #include "config.h"
  22
  23 #include <math.h>
  24 #include <stdlib.h>
  25
  26 #include "AL/al.h"
  27 #include "alFilter.h"
  28 #include "alAuxEffectSlot.h"
  29 #include "alEcho.h"
  30 #include "alu.h"
  31
  32 struct ALechoState {
  33     ALfloat *SampleBuffer;
  34     ALuint BufferLength;
  35
  36     // The echo is two tap. The third tap is the offset to write the feedback
  37     // and input sample to
  38     struct {
  39         ALuint offset;
  40     } Tap[3];
  41     // The LR gains for the first tap. The second tap uses the reverse
  42     ALfloat GainL;
  43     ALfloat GainR;
  44
  45     ALfloat FeedGain;
  46
  47     FILTER iirFilter;
  48     ALfloat history[2];
  49 };
  50
  51 // Find the next power of 2.  Actually, this will return the input value if
  52 // it is already a power of 2.
  53 static ALuint NextPowerOf2(ALuint value)
  54 {
  55     ALuint powerOf2 = 1;
  56
  57     if(value)
  58     {
  59         value--;
  60         while(value)
  61         {
  62             value >>= 1;
  63             powerOf2 <<= 1;
  64         }
  65     }
  66     return powerOf2;
  67 }
  68
  69 ALechoState *EchoCreate(ALCcontext *Context)
  70 {
  71     ALechoState *state;
  72     ALuint i, maxlen;
  73
  74     state = malloc(sizeof(*state));
  75     if(!state)
  76         return NULL;
  77
  78     maxlen  = (ALuint)(AL_ECHO_MAX_DELAY * Context->Frequency);
  79     maxlen += (ALuint)(AL_ECHO_MAX_LRDELAY * Context->Frequency);
  80
  81     // Use the next power of 2 for the buffer length, so the tap offsets can be
  82     // wrapped using a mask instead of a modulo
  83     state->BufferLength = NextPowerOf2(maxlen+1);
  84     state->SampleBuffer = malloc(state->BufferLength * sizeof(ALfloat));
  85     if(!state->SampleBuffer)
  86     {
  87         free(state);
  88         return NULL;
  89     }
  90
  91     for(i = 0;i < state->BufferLength;i++)
  92         state->SampleBuffer[i] = 0.0f;
  93
  94     state->Tap[0].offset = 0;
  95     state->Tap[1].offset = 0;
  96     state->Tap[2].offset = 0;
  97     state->GainL = 0.0f;
  98     state->GainR = 0.0f;
  99
 100     for(i = 0;i < sizeof(state->history)/sizeof(state->history[0]);i++)
 101         state->history[i] = 0.0f;
 102     state->iirFilter.coeff = 0.0f;
 103
 104     return state;
 105 }
 106
 107 ALvoid EchoDestroy(ALechoState *state)
 108 {
 109     if(state)
 110     {
 111         free(state->SampleBuffer);
 112         state->SampleBuffer = NULL;
 113         free(state);
 114     }
 115 }
 116
 117 ALvoid EchoUpdate(ALCcontext *Context, struct ALeffectslot *Slot, ALeffect *Effect)
 118 {
 119     ALechoState *state = Slot->EchoState;
 120     ALuint newdelay1, newdelay2;
 121     ALfloat lrpan, cw, a, g;
 122
 123     newdelay1 = (ALuint)(Effect->Echo.Delay * Context->Frequency);
 124     newdelay2 = (ALuint)(Effect->Echo.LRDelay * Context->Frequency);
 125
 126     state->Tap[0].offset = (state->BufferLength - newdelay1 - 1 +
 127                             state->Tap[2].offset)%state->BufferLength;
 128     state->Tap[1].offset = (state->BufferLength - newdelay1 - newdelay2 - 1 +
 129                             state->Tap[2].offset)%state->BufferLength;
 130
 131     lrpan = Effect->Echo.Spread*0.5f + 0.5f;
 132     state->GainL = aluSqrt(     lrpan);
 133     state->GainR = aluSqrt(1.0f-lrpan);
 134
 135     state->FeedGain = Effect->Echo.Feedback;
 136
 137     cw = cos(2.0*M_PI * LOWPASSFREQCUTOFF / Context->Frequency);
 138     g = 1.0f - Effect->Echo.Damping;
 139     a = 0.0f;
 140     if(g < 0.9999f) // 1-epsilon
 141         a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) / (1 - g);
 142     state->iirFilter.coeff = a;
 143 }
 144
 145 ALvoid EchoProcess(ALechoState *state, ALuint SamplesToDo, const ALfloat *SamplesIn, ALfloat (*SamplesOut)[OUTPUTCHANNELS])
 146 {
 147     const ALuint delay = state->BufferLength-1;
 148     ALuint tap1off = state->Tap[0].offset;
 149     ALuint tap2off = state->Tap[1].offset;
 150     ALuint fboff = state->Tap[2].offset;
 151     ALfloat samp[2];
 152     ALuint i;
 153
 154     for(i = 0;i < SamplesToDo;i++)
 155     {
 156         // Apply damping
 157         samp[0] = lpFilter2P(&state->iirFilter, 0, state->SampleBuffer[tap2off]+SamplesIn[i]);
 158
 159         // Apply feedback gain and mix in the new sample
 160         state->SampleBuffer[fboff] = samp[0] * state->FeedGain;
 161
 162         tap1off = (tap1off+1) & delay;
 163         tap2off = (tap2off+1) & delay;
 164         fboff = (fboff+1) & delay;
 165
 166         // Sample first tap
 167         samp[0] = state->SampleBuffer[tap1off]*state->GainL;
 168         samp[1] = state->SampleBuffer[tap1off]*state->GainR;
 169         // Sample second tap. Reverse LR panning
 170         samp[0] += state->SampleBuffer[tap2off]*state->GainR;
 171         samp[1] += state->SampleBuffer[tap2off]*state->GainL;
 172
 173         SamplesOut[i][FRONT_LEFT]  += samp[0];
 174         SamplesOut[i][FRONT_RIGHT] += samp[1];
 175         SamplesOut[i][SIDE_LEFT]   += samp[0];
 176         SamplesOut[i][SIDE_RIGHT]  += samp[1];
 177         SamplesOut[i][BACK_LEFT]   += samp[0];
 178         SamplesOut[i][BACK_RIGHT]  += samp[1];
 179     }
 180
 181     state->Tap[0].offset = tap1off;
 182     state->Tap[1].offset = tap2off;
 183     state->Tap[2].offset = fboff;
 184 }