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
  31 #ifdef HAVE_SQRTF
  32 #define aluSqrt(x) ((ALfloat)sqrtf((float)(x)))
  33 #else
  34 #define aluSqrt(x) ((ALfloat)sqrt((double)(x)))
  35 #endif
  36
  37 struct ALechoState {
  38     ALfloat *SampleBuffer;
  39     ALuint BufferLength;
  40
  41     // The echo is two tap. The third tap is the offset to write the feedback
  42     // and input sample to
  43     struct {
  44         ALuint offset;
  45     } Tap[3];
  46     // The LR gains for the first tap. The second tap uses the reverse
  47     ALfloat GainL;
  48     ALfloat GainR;
  49
  50     ALfloat FeedGain;
  51     FILTER iirFilter;
  52 };
  53
  54 // Find the next power of 2.  Actually, this will return the input value if
  55 // it is already a power of 2.
  56 static ALuint NextPowerOf2(ALuint value)
  57 {
  58     ALuint powerOf2 = 1;
  59
  60     if(value)
  61     {
  62         value--;
  63         while(value)
  64         {
  65             value >>= 1;
  66             powerOf2 <<= 1;
  67         }
  68     }
  69     return powerOf2;
  70 }
  71
  72 ALechoState *EchoCreate(ALCcontext *Context)
  73 {
  74     ALechoState *state;
  75     ALuint i, maxlen;
  76
  77     state = malloc(sizeof(*state));
  78     if(!state)
  79         return NULL;
  80
  81     maxlen  = (ALuint)(AL_ECHO_MAX_DELAY * Context->Frequency);
  82     maxlen += (ALuint)(AL_ECHO_MAX_LRDELAY * Context->Frequency);
  83
  84     // Use the next power of 2 for the buffer length, so the tap offsets can be
  85     // wrapped using a mask instead of a modulo
  86     state->BufferLength = NextPowerOf2(maxlen+1);
  87     state->SampleBuffer = malloc(state->BufferLength * sizeof(ALfloat));
  88     if(!state->SampleBuffer)
  89     {
  90         free(state);
  91         return NULL;
  92     }
  93
  94     for(i = 0;i < state->BufferLength;i++)
  95         state->SampleBuffer[i] = 0.0f;
  96
  97     state->Tap[0].offset = 0;
  98     state->Tap[1].offset = 0;
  99     state->Tap[2].offset = 0;
 100     state->GainL = 0.0f;
 101     state->GainR = 0.0f;
 102
 103     for(i = 0;i < sizeof(state->iirFilter.history)/sizeof(state->iirFilter.history[0]);i++)
 104         state->iirFilter.history[i] = 0.0f;
 105     state->iirFilter.coeff = 0.0f;
 106
 107     return state;
 108 }
 109
 110 ALvoid EchoDestroy(ALechoState *state)
 111 {
 112     if(state)
 113     {
 114         free(state->SampleBuffer);
 115         state->SampleBuffer = NULL;
 116         free(state);
 117     }
 118 }
 119
 120 ALvoid EchoUpdate(ALCcontext *Context, struct ALeffectslot *Slot, ALeffect *Effect)
 121 {
 122     ALechoState *state = Slot->EchoState;
 123     ALuint newdelay1, newdelay2;
 124     ALfloat lrpan, cw, a, g;
 125
 126     newdelay1 = (ALuint)(Effect->Echo.Delay * Context->Frequency);
 127     newdelay2 = (ALuint)(Effect->Echo.LRDelay * Context->Frequency);
 128
 129     state->Tap[0].offset = (state->BufferLength - newdelay1 - 1 +
 130                             state->Tap[2].offset)%state->BufferLength;
 131     state->Tap[1].offset = (state->BufferLength - newdelay1 - newdelay2 - 1 +
 132                             state->Tap[2].offset)%state->BufferLength;
 133
 134     lrpan = Effect->Echo.Spread*0.5f + 0.5f;
 135     state->GainL = aluSqrt(     lrpan);
 136     state->GainR = aluSqrt(1.0f-lrpan);
 137
 138     state->FeedGain = Effect->Echo.Feedback;
 139
 140     cw = cos(2.0*M_PI * LOWPASSFREQCUTOFF / Context->Frequency);
 141     g = 1.0f - Effect->Echo.Damping;
 142     a = 0.0f;
 143     if(g < 0.9999f) // 1-epsilon
 144         a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) / (1 - g);
 145     state->iirFilter.coeff = a;
 146 }
 147
 148 ALvoid EchoProcess(ALechoState *state, ALuint SamplesToDo, const ALfloat *SamplesIn, ALfloat (*SamplesOut)[OUTPUTCHANNELS])
 149 {
 150     ALfloat *history = state->iirFilter.history;
 151     const ALfloat a = state->iirFilter.coeff;
 152     const ALuint delay = state->BufferLength-1;
 153     ALuint tap1off = state->Tap[0].offset;
 154     ALuint tap2off = state->Tap[1].offset;
 155     ALuint fboff = state->Tap[2].offset;
 156     ALfloat samp[2];
 157     ALuint i;
 158
 159     for(i = 0;i < SamplesToDo;i++)
 160     {
 161         // Apply damping
 162         samp[0] = state->SampleBuffer[tap2off] + SamplesIn[i];
 163
 164         samp[0] += (history[0]-samp[0]) * a;
 165         history[0] = samp[0];
 166         samp[0] += (history[1]-samp[0]) * a;
 167         history[1] = samp[0];
 168
 169         // Apply feedback gain and mix in the new sample
 170         state->SampleBuffer[fboff] = samp[0] * state->FeedGain;
 171
 172         tap1off = (tap1off+1) & delay;
 173         tap2off = (tap2off+1) & delay;
 174         fboff = (fboff+1) & delay;
 175
 176         // Sample first tap
 177         samp[0] = state->SampleBuffer[tap1off]*state->GainL;
 178         samp[1] = state->SampleBuffer[tap1off]*state->GainR;
 179         // Sample second tap. Reverse LR panning
 180         samp[0] += state->SampleBuffer[tap2off]*state->GainR;
 181         samp[1] += state->SampleBuffer[tap2off]*state->GainL;
 182
 183         SamplesOut[i][FRONT_LEFT]  += samp[0];
 184         SamplesOut[i][FRONT_RIGHT] += samp[1];
 185         SamplesOut[i][SIDE_LEFT]   += samp[0];
 186         SamplesOut[i][SIDE_RIGHT]  += samp[1];
 187         SamplesOut[i][BACK_LEFT]   += samp[0];
 188         SamplesOut[i][BACK_RIGHT]  += samp[1];
 189     }
 190
 191     state->Tap[0].offset = tap1off;
 192     state->Tap[1].offset = tap2off;
 193     state->Tap[2].offset = fboff;
 194 }