// returns factor
static double normalizeShortArrays(L<short[]> l) {
  int max = min(32767, absShortMax_multipleArrays(l));
  if (max == 0 || max == 32767) ret 1;
  double factor = 32767.0/max;
  for (short[] a : l)
    for i over a:
      a[i] = roundToShort(a[i]*factor);
  ret factor;
}