If you listen to the Astros' AAA affiliate Oklahoma City during the 2013 season, the voice you will hear is Alex Freedman. The above clip is of Freedman in action during a 2012 RedHawk game against Albuquerque on August 28.
Freedman took over the play-by-play duties for Oklahoma City during the 2012 season. His Twitter handle is @azfreedman. Freedman starts calling RedHawks games on April 4.