So how do I play the musical instruments? and my companions also? summons may be?

[Sephiroth]

I seen someone mention it before and I havent done it yet.

[Simpson3k]

To me the instruments look like a feature they wanted to be a part of the game since the beginning but then they forgot about it but left it in the char creation because they didnt care ^^

[Carnasid]

The instrument selection alters various music tracks, typically in combat.

[number30five]

i think i noticed the sound played when you switch party members changes depending on what instrument you picked for them.

like, my PC, Ifan picked the cello. so, when i select him, a short cello melody plays. when i pick Sibelle, a short lute thing plays.

then again... i may have imagined this. it's very subtle.

[Zunnoab #931]

The differences are pretty notable sometimes too. The instruments don't necessarily use the exact same melody in variations of the songs.

[Firecam]

It plays when you kill someone for exemple.

[Zunnoab #931]

There are a bunch of versions of Dancing with the Source that are quite distinct from each other depending on the instrument. I confess I didn't even recognize it as the same song as the 'default' version vs. the instrument-chosen versions. It's obvious now that I know, but the melodies are quite different.

Edit:
Wait the version outright changes as you make killing blows? That's interesting if so. I wish more games would do that. Grant Kirkhope does that all the time in his soundtracks.

[Damashi The Kaotic]

When you get a kill in combat it changes the song that plays during combat to match the instrament you choose. Some songs out in the world also changed based on what origin instrament you use.

[Gwumpy Fwog]

they are drastic changes.... how do ppl not notice them lol?
https://www.youtube.com/watch?v=58yMg8xPh9I - Cello

https://www.youtube.com/watch?v=F1DLmPtn9MA - Oud