What is the pianist in "The Weary Blues" doing when he makes the piano "moan with melody"?

What is the setting of this passage by jack london? the call of the wild buck lived at a big house in the sun-kissed santa clara valley. judge miller’s place, it was called. it stood back from the road, half hidden among the trees. glimpses could be caught through the trees of the wide, cool veranda that ran around all four sides of the house. the house was approached by gravel driveways, which wound through wide lawns and under the connecting boughs of tall poplar trees.