Tā tiáozhěng luóxuán, gǎibiàn dìngyīngǔ de yīngāo.
He adjusts the screws to change the pitch of the timpani.
Tips
memory
定 (fix/tune) + 音 (pitch) + 鼓 (drum) = a drum whose pitch is fixed. That literal reading is exactly what makes a timpani different from an ordinary drum — you can tune it.
