This is the next in my series of musical puzzles. I hope you find this puzzle entertaining, and perhaps a bit more challenging than my last.
When you are looking for the cache, do NOT do what this hand is doing. The cache is NOT in that tree!

You will first need to listen to a mystery tune.
The cache is not at the posted coordinates; solve the puzzle below to find the final destination.
Mystery tune
This solo is from a very popular (and funny) opera. It is one of the most well known (and difficult) arias for a baritone singer. The aria is known by a short (Italian) phrase.
Cache location: N37 42.AB1 W121 57.CD6
A= # of letters in last name of opera composer - 4
B= # of letters in main character's name + 2
C= # of letters in main character's occupation - 6
D= # of letters in first word of aria name - 3
Checksum: A+B+C+D = 13
You will know you are in the right place when you come to a nice, shady glen.
Congrats FTF to dprovan!