static float pcmToLevel(byte[] pcm) {
  float sum = 0, max = 0;
  for i over pcm: {
    int p = (int) pcm[i];
    float l = abs(p)/128f;
    sum += l;
    max = max(max, l);
  }
  //float l = sum/pcm.length;
  float l = max;
  //print(bytesToHex(pcm) + " " + l);
  ret l;
}