DSP Applications and Student Projects - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 354

// Beatdetector.c Core program for beat detection project

const int chunks = 20; //number of frames in buffer

const int instant_length = 200; //length of 1 buffer

#define average_length 4000 //length of buffer

const float c = 1.3; //confidence multiplier

double ae = 0, ie = 0;
short buffer[average_length]; //Buffer

void main()
{
comm_poll(); //init DSK, codec, McBSP
while(average_counter < average_length){ //sample entire buffer

buffer[average_counter] = input_sample();

average_counter++;

}
while(1) { //infinite loop

instant_counter = 0;
while(instant_counter<instant_length){ //sample one frame and
buffer[chunk_counter*instant_length+instant_counter]=input_sample();
instant_counter++; //move it to circular buffer
}
for (average_counter=0;average_counter<average_length;average_counter++) {
ae=ae+buffer[average_counter]*buffer[average_counter];//av energy
} //in entire buffer
ae = ae / average_length;
for (instant_counter=0;instant_counter<instant_length;instant_counter++) {
ie=ie+buffer[chunk_counter*instant_length+instant_counter]
*buffer[chunk_counter*instant_length+instant_counter];
} //average energy in last few msec

ie = ie / instant_length;
if (ie > ae*c){//if energy in short buffer>whole buffer,turn on LEDs
..
else { //if not, turn off LEDs

..
}
chunk_counter++; //incr position in chunk counter
if(chunk_counter>=chunks) chunk_counter=0; //right point in buffer
}

//end of while(1) infinite loop

} //end of main

FIGURE 10.6. Core C program for beat detection ( beatdetector.c ).

2. The larger the buffer, the longer the processing time for calculating the
average energy, so the buffer size is limited by the processing speed of the
board.
3. A larger buffer requires the use of external memory, which can mean a reduc-
tion in speed.

A buffer stored in internal memory with a length of half a second (4000 points)
decomposed into 20 chunks seems to work best. The LEDs onboard the DSK are
flashed whenever a beat is detected. To expand on this project, the beat informa-