Final answer:
The trombone is the instrument that accompanies the baritone in the "Tuba mirum" section of Mozart's Requiem, not a tuba. The section's name translates to "wonderful horn", but refers to the trombone, as the tuba wasn't invented at the time. Smaller instruments produce higher pitches due to faster vibration frequencies.
Step-by-step explanation:
The instrument that accompanies the baritone voice in the "Tuba mirum" section of Mozart's Requiem is the trombone. This is a distinctive feature of this movement, where the trombone solo interacts with the baritone soloist, following the theme of the Last Judgement. The name 'Tuba mirum', which might suggest the use of a tuba, is actually misleading in this context, as the tuba did not exist at the time when Mozart composed his Requiem.
In response to Question 65 regarding why smaller instruments produce higher-pitched sounds compared to larger instruments: It is because the pitch of a sound is largely determined by the frequency of the sound wave produced. Smaller instruments like the piccolo have shorter air columns or strings that vibrate at higher frequencies, thus producing higher pitches. Larger instruments, like tubas, have longer air columns or strings which vibrate at lower frequencies, resulting in lower pitches.