system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does it mean when music is played in a specific note such as "Pachelbel Canon in D"?

Can the songs be played in other notes or would it sound awful or strange?
gpt
D was the "key" chosen.  D is the base note and it follows the scale up to D by going through the notes D E F# G A B C# D

Pachelbel's Canon was originally written for 3 violins and accompaniment (cello, harpsichord, etc).  The violin sounds really great in D major because of how its strings are tuned.

They certainly could move the piece to a different key (called transposing).  It wouldn't sound as good on a violin, but maybe if different instruments are used instead.

Composers write keys in different keys for a wide variety of reasons.  Different instruments sound "stronger" in different keys.  But sometimes they just write in a different key to give them new ideas.  A key will 'feel' different to a player.  Certain melodies are more apt. It just freshens things up to use different keys from time to time.