Via Mashable, in turn via technewsdaily, in turn referencing the source, Professor John G. Taylor, Department of Physics, University of Washington, the 2013 Planck Version of The Sound of the Big Bang.
Scroll down his page for explanation. Key point in my view:
The sound frequencies used in the simulation must be scaled upward by a huge factor (about 10 to the 26 power) to match the response of the human ear, because the actual Big Bang frequencies, which had wavelengths on the order of a fraction of the size of the universe, were far too low to be heard by humans (even had any been around).
10 to the 25th power is: one hundred million million million million