void playPattern(int *timer, int duration, int *step) {
  *timer = *timer >= duration ? 0 : *timer+1;
  usleep(1000);

  if(*timer == 0) {
    for(int i=0; i<matrix[0]; i++) {
      if(pattern[i][*step-1]-'0' == 1) {
        Mix_PlayChannel(-1, samples[i], 0);
      }
    }
    *step = *step < matrix[1]-1 ? *step+1 : 1;
  }
}

void playSample(int sample) {
  Mix_PlayChannel(-1, samples[sample-1], 0);
}