Frühlingsstimmen (or Voices of Spring) was a waltz composed by Johann Strauss II of Earth in the 19th century.
The Doctor kept the waltz stored under the name "EMH music file gamma 12". When The Doctor was trapped in Seven of Nine's body to evade Lokirrim detection, he/she dimmed the light in the Delta Flyer, replicated some champagne, and danced to the Frühlingsstimmen waltz with the Lokirrim Captain Ranek to get close enough to stun him. (VOY: "Body and Soul")