During the hoopla leading up to the Las Vegas Philharmonic’s first performance at the Smith Center, conductor David Itkin and certain musicians kept hyping “the sound.” And they were right. It’s crystal clear. Perfect, even. Saturday’s performance of Mahler’s Second Symphony was as if the city got a brand new orchestra thrown in with the Smith Center package. It raised the stature of the Philharmonic to a new level in one performance, as musicians delivered their dramatic range of tempos and dynamics in the five-movement “Resurrection.” But something else happened that night, something beautiful. The vocals. Three Las Vegas choirs, along with two operatic soloists—soprano Marie Plette and mezzo-soprano Eugenie Grunewald—made it seem as if Reynolds Hall had been specifically designed for the pureness of human voice.