  The fitting formula for the location of the first acoustic peak in the matter
power spectrum is revised. We discuss the physics that leads to baryon acoustic
oscillations: the recombination history, the tight coupling approximation and
the velocity overshoot effect. A new fitting formula is proposed, which is in
accordance within 5% with numerical results for a suitable range of
cosmological parameters, whereas previous results yield deviations of up to
20%. The crucial improvement turns out to be the accuracy of the recombination
history.
