I guess there are tons of different Bard classes out there between the ever-growing amount of editions and home-brewed classes. Here's my attempt to introduce a new game play mechanic to 17th century fantasy gaming.
Bards begin spellcasting by selecting a Motif. This is the base effect that will be further modified as the Bard performs. For example:
Coraggio: A piece that affects courage to those who hear it.
The performance can be in either minor or major key. The major key is an uplifting, positive tone whereas the minor key is a dark and melancholic tone. In game terms, the base Motif will have a positive or negative effect. For example:
Coraggio (Major): bonus to morale
Coraggio (Minor): malus to morale
Each performance can have one of three accompaniments, which essentially affects the magnitude of its effects (oh, there's a grammar lesson for you). One example might be:
A capella: +/- 1 to morale
Cantata: Reroll a morale check
Concerto: Force a morale check
Each motif then is six potential spells; Bards gain motifs per level as a spellcaster gains spells. Maybe a Bard learns one Motif per level. He can always module that Motif in either key. Then, he can sing its weakest effect, play an instrument with the vocals for a greater affect, or play in a troupe of bards for a stupendous effect.
Accompaniments are probably gained as a function of level, so a first level Bard can only perform a capella, a third level bard can perform a cantata to accompany (his own or other?) vocals, and a fifth level bard can lead 2 other Bards (at least one of which is at 3rd level) by playing a concerto. The level up mechanic would most likely increase the range or amount of HD affected.
There's plenty of ground here to come up with tons of motifs. The idea needs some fleshing out, but building on this foundation could be a fun exercise.
I think it is a neat mechanic, what do you think?
[Forgive me for massacring the terminology, I'm obviously not in the music world]