Many thanks to Steve for submitting detailed information about the Source of the Sample at 02:58, suggesting that this may be Deems Taylor: (1885-1966, a U.S. composer and music critic) providing commentary for the Mercury Living Presence Stereo recording of Tchaikovsky's 1812 Overture (with real cannons!). It certainly sounds like the voice of Deems Taylor, though I cannot find the exact quote on the 1812 Overture album. It may be that this sample is from an outake of that recording.
Do you know?