Audio from a video recording captures what is believed to be the sonic
boom (heard at 00:25 in this clip) made by Felix Baumgartner as he broke
through the speed of sound barrier. The footage was recorded using a
video camera pointing skyward as Baumgartner accelerated to a speed of
833.9 mph (1,342.8 km/h) during his jump from the edge of space. The
'wave form' of the sonic boom was isolated and analysis found it to be
consistent with existing ‘sonic boom characteristics’ data. Project
Director Art Thompson is now working closely with sound experts who are
also examining GPS data and other telemetry information from the chest
pack to verify Baumgartner’s speed and timing of the sonic boom. They
are using the same algorithm that NASA applies to work out the exact
moment an object travels though the sound barrier. This scientific
evidence is backed up by four different groups of observers on the
ground that stated they heard the sonic boom.

For more information: http://www.redbullstratos.com/ and http://www.redbull.com/cs/Satellite/en_INT/Video/Red-Bull-Stratos-Felix-Baumgartner%E2%80%99s-sonic-boom-021243275206411