“This is Louis ‘Satchmo’ Armstrong,” the voice resounds, “talking to all the kids from all over the world at Christmastime.” With that, the trumpeter and singer tucks into a lyrical, buoyant reading of “The Night Before Christmas.” He hews to the words but makes them his own in a voice that glitters with joy. When the 69-year-old describes Santa’s “little round belly /that shook when he laughed like a bowl of jelly,” he breaks into a wheezy giggle that sounds like a truck rumbling to life at a green light.