Most people, even most musicians who have not had formal musical education at the college or university level, do not know what musical dictation is. But for those who do know what it is and have to do it, it is often the bane of their musical existence. Musical dictation is the skill of hearing something and being able to write it down just as played. Dictation can be separated into three categories: harmonic dictation, melodic dictation, and rhythmic dictation.
Harmonic dictation is the ability to hear a chord and know which degree of the scale it is built on and which inversion, if any, it is voiced in. Harmonic dictation is often easier for musicians who play instruments that play chords, such as pianos.
Melodic dictation is the ability to hear a single melodic line and write it down just as heard. Melodic dictation is usually easier than harmonic dictation.
Rhythmic dictation is the ability to hear and write down rhythms instead of notes. Depending on the musician, this might be much harder or much easier than harmonic or melodic dictation.
There are several reasons why dictation is such a hard part of musicianship. One is that most musicians do nothing to develop their critical listening ear before entering a class where they are required to do dictation. Another reason is that even people with good ears can get confused with dictation, and having no way to concretely know if they are right in their dictation-taking, not be very confident in their dictation skills. But like most things in music, dictation skills are difficult and sometimes monotonous to develop, but in the end are essential and worthwhile assets to one’s musical skills.