Minor Magical Focus : Music ?

Greetings everyone,

I just picked up my good old arsmagica books to start a new saga. One of the mages plays a bard Merinita and ask for the virtue Minor Magical Focus : Music.
By the guidelines of magical focus in imaginem music is certainly less than a major magical focus but I think it's a bit too vast for the minor version that said (a particular sound). So which one would it be ?

Second question, that magus have Performance Magic (music) so he can replace vocal and gestual components by playing his instrument so he can affect emotions (mentem) subtly while playing music.

Does a magical focus apply to:
a) any spells he cast by playing music (replacing somatic and vocal spell casting by performing music).
b) any spells with the special duration(performance) (see Performance Magic)
c) spells linked to musical instruments.

Thanks for your help !

My take is that the focus affects any spell that targets the focus but not magic that incidentally includes the focus; eg. A magical focus with swords can be used to cast spells on swords such as spells to control swords, spells to create swords or spells to make swords sharper, but the focus bonus could not be applied a lab total to enchant a sword with the ability to change ducks into orangutans at range voice.

By that yardstick I think that only the duration song spells might apply and perhaps not even those.

It might apply to a wacky duration song version of maintain the demanding spell.