These crystals, when utilised in armour or a weapon, produce a certain tone when the a weapon strikes or the armour is struck. The volume is proportional to the force imparted in the blow, and the tone produced is either dependant on the location of contact on the armour/weapon, or produces the same tone/chord/dissonant jumble of notes every time due to crystal resonance. Note: This would allow a particularly skilled fighter/musician to perform songs in combat while only focusing on the combat itself, or in the case if dissonance temporarily stun sound-sensitive foes.
Nope, it turns armour/weapons into a musical instrument. While I suppose this could be used as crimson granite/memory metal for songs, the original intention was so that song-based characters wouldn't have to sit back and play a musical instrument in order to get the full benefit. Admittedly, the most enjoyable moment in Skyward Sword for me was when I had link running away from all the moblins during that Ghirahim's gauntlet bit whole playing his harp, but I'd like for characters to have the opportunity to attack the boss AND provide the benefits of their song.
A material that allows armor or a weapon (or from the sound of it virtually any solid object) into a percussion instrument is a neat idea. That said, I would want to clarify that playing the weapon-instrument in combat or movement would be (and should be) virtually impossible. Many songs are balanced by the fact the player has to stop and play them--particularly those which heal. With this material as written, someone could just repeatedly play the Sonata of Soothing while beating people up, effectively constantly healing their injuries. Even barring that, most songs require 'skillful playing' to work. It is intentionally difficult to play most songs well enough for them to be used. Someone who could not only play this songs on a primitive instrument, but do so while moving around and fighting, requires an unrealistic level of talent--the sort of thing that would need to be a treasure in its own right. (Not that it would be a treasure, because, again, many songs are balanced by the fact the player needs to stop and focus on playing.) So. I can add Tune Crystals as a magical material that can turn an item crafted from it into an instrument, but it still will not be possible to play treasure-tier songs while fighting.
Yeah, that's pretty legit. I also like the idea of a minstrel disguised as a merchant guard, and during a bandit attack... "Wait, what's that music?" "OH NO! That man isn't a bodyguard, he's a minstrel in disguise! RUN AWAY" Or in other words a reversal of a pretty common trope.
Alright, then. It has been added accordingly: http://library.hyrulecastle.org/index.php?title=Tune_Crystal_(Material)
