What is the hardest brass instrument to play?

The French horn is often considered one of the hardest brass instruments to play due to its small mouthpiece, conical shape, and complex inner tubing. It requires great technique and control to produce a clear and resonant sound, as well as a strong embouchure to navigate the wide range of notes and dynamic levels. The horn also has a tendency to be out of tune, which requires the player to constantly adjust their pitch through hand placement in the bell. Additionally, the horn is known for its challenging orchestral repertoire, which often features intricate and high-pitched solos requiring dexterity and precision. Overall, mastering the French horn can be a long and difficult process that requires dedication, patience, and consistent practice.