Beat Detection on iPhone with wav files and openal
- by Dmacpro
Using this website i have tried to make a beat detection engine. http://www.gamedev.net/reference/articles/article1952.asp
{
ALfloat energy = 0;
ALfloat aEnergy = 0;
ALint beats = 0;
bool init = false;
ALfloat Ei[42];
ALfloat V = 0;
ALfloat C = 0;
ALshort *hold;
hold = new ALshort[[myDat length]/2];
[myDat getBytes:hold length:[myDat length]];
ALuint uiNumSamples;
uiNumSamples = [myDat length]/4;
if(alDatal == NULL)
alDatal = (ALshort *) malloc(uiNumSamples*2);
if(alDatar == NULL)
alDatar = (ALshort *) malloc(uiNumSamples*2);
for (int i = 0; i < uiNumSamples; i++)
{
alDatal[i] = hold[i*2];
alDatar[i] = hold[i*2+1];
}
energy = 0;
for(int start = 0; start<(22050*10); start+=512){ //detect for 10 seconds of data
for(int i = start; i<(start+512); i++){
energy+= fabs(alDatal[i]) + fabs(alDatar[i]);
}
aEnergy = 0;
for(int i = 41; i>=0; i--){
if(i ==0){
Ei[0] = energy;
}
else {
Ei[i] = Ei[i-1];
}
if(start >= 21504){
aEnergy+=Ei[i];
}
}
aEnergy = aEnergy/43.f;
if (start >= 21504) {
for(int i = 0; i<42; i++){
V += (Ei[i]-aEnergy);
}
V = V/43.f;
C = (-0.0025714*V)+1.5142857;
init = true;
if(energy >(C*aEnergy)) beats++;
}
}
}
alDatal and alDatar are (short*) type;
myDat is NSdata that holds the actual audio data of a wav file formatted to
22050 khz and 16 bit stereo.
This doesn't seem to work correctly. If anyone could help me out that would be amazing. I've been stuck on this for 3 days.
