Ten years ago when the WMAP data on the cosmic microwave background (CMB) became available, John Cramer, Professor Emeritus of Physics at the University of Washington, completed a Mathematica calculation to produce "the sound of the Big Bang." Cramer decided to do the same thing with the new data from the ESA's Planck Mission analysis of the CMB, which analyzes the temperature variations of the cosmic microwave background into angular frequency components or multipoles. The new frequency spectrum goes to much higher frequencies than did the WMAP analysis, and therefore offers a more "high-fidelity" rendition of the Sound of the Big Bang.
How fast the universe initially expanded depends on what cosmological model is used. Cramer follows the predictions of the flat-space Robertson-Walker metric with zero cosmological constant. That model predicts that the radius of the universe grows as time to the 2/3 power (R ~ t2/3). Therefore, instead of the component sine waves varying as (frequency ´ time), they vary as (frequency ´ time1/3) to implement the cosmological Doppler shift. 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, would have been far too low to be heard by humans.
The Sound of the Big Bang simulation includes three important effects: (1) The multiply peaked frequency spectrum measured by Planck is made into a single sound wave (monaural, not stereo) by the process described above; (2) According to the Planck analysis, the emission profile of the cosmic background radiation peaked at 379,000 years and dropped to 60% intensity at 110,000 years before and after the peak emission time. The Planck multipole spectrum looks like this: