Several characters appear in both this short and the earlier short 'The Band Concert.' Interestingly, none of them play the same instruments in both cartoons (Mickey led the band in both films, however).
The piece being played is the "Light Cavalry Overture" by Franz von Suppé.
This is the only Mickey Mouse cartoon to feature Mickey Mouse actually threatening to shoot Donald Duck with a handgun. The scene was removed from television showings in 2000.
"Symphony Hour" from 1942 is the last appearance of both Horace Horsecollar, Clarabelle Cow and Clara Cluck in a Mickey Mouse Cartoon until the 1983 Mickey Mouse featurette "Mickey's Christmas Carol (1983)", 41 years later. However, they only have cameo appearances in "Mickey's Christmas Carol" from 1983.
Pete's character as Sylvester Macaroni in "Symphony Hour" from 1942 caused a bit of controversy with the Italian community in which they felt that Macaroni was an unfair stereotype on their behalf, considering the fact that he had a thick Italian accent and chain-smoked cigars. This was not the first time that a character (especially Pete) had been attacked due to their portrayal of another character.