Anyone who has listened to a skilled musician knows that there is some form of magic there. A magic that, try though we have, has not been properly represented in Roleplaying games. Here is an attempt to change that.
For the purposes of this, types of music can be broken down into a number of different types:
Vocals: The abilities of a mage-singer differ depending on whether they are primarily a bass or soprano. (while there are many more types, these are the two significant ones for our purposes)
Bass singing is powerful, carrying the force of a wrecking ball in some cases. It can be hard to be accurate with, and even in the best cases causes a large amount of collateral damage. A bassist may not be able to pinpoint a glass to shatter, but would shatter the table it was on, possibly with some of the chairs.
Sopranos lack much area of effect, but are capable of punching through very tough materials. Whereas bass singing is like a wrecking ball, soprano is like a arrow. A skilled soprano is actually capable of punching through metal.
String: The lute, guitar, fiddle, cello and many more fall into this category. There are too many to get very specific, but a few deserve special note.
Most string instruments, when used offensively, are capable of slicing things to shreds. Each note may cause very little damage, but it is when a song is played that the damage becomes worrisome. Often by the end of the first chorus, the object in question has sustained notable damage, and small objects can be broken by this point. A long, fast song can be horribly devastating.
Fiddles and other string instruments played with a bow are slightly different, as they don’t operate by individual plucked notes. Instead, they are almost a continuous wave. When played, they build a sort of momentum, the slicing effects getting more and more effective the longer the instrument is played without stopping. However, if the player stops even for a moment, their momentum is lost. The baseline damage for these instruments is lower than that of plucked instruments, but they are capable of devastating power if played long enough.
Woodwind: Flutes, oboes and their ilk would fall into this category. While they are often of little effect on their own, they become significant when played along with another instrument. (Not necessarily by the same player, simply supporting another instrument.) They seem to magnify the effects of both instruments, and even the damage that this type does is the same as the supported type.
Brass: This is the domain of trumpets, tubas and piccolos. Brass instruments possess a piercing note that carries unusually far, though they tend to be a little inaccurate at closer ranges. Generally, the deeper the note, the wider the area of effect and the less damage to an equivalent area. (i.e. a tuba could cover a large area, but the amount of damage inflicted on a square inch would be much less than if that same spot was hit with a piccolo, though the piccolo would likely only hit the one spot.)
Percussion: The domain of drums and xylophones. For causing damage to an inanimate object, there is nothing better than a good, big drum. The effects on living things is notable, but usually limited to causing them to fall down when the ground beneath them begins to shake. Primarily, percussion instruments are best described as sonic siege engines, they can blow through a wall much easier than a person, much like a battering ram.
Other: There are other instruments that don’t really fit in the other categories, such as bagpipes, accordions and pianos.
Bagpipes are a terrifying thing to hear, whether or not the user is any good. Only a skilled user can bring out the magic in them, though. A very hard instrument to learn, it is nonetheless quite powerful if used properly. Sometimes referred to as a ‘Hydra call’ it’s capable of lashing out in multiple directions at the same time. Also notable is the fact that the damage it causes is a blend of crushing and slicing damage. A skilled user can keep many foes at bay, and if he focuses on one or two actually push them around at his will. The biggest weakness of this weapon is that any damage whatsoever to the bag will effectively ruin it, at least until repaired.
Accordions are a peculiar instrument that rarely sees much use in combat, generally due to their size. When used, they produce a large area of slicing damage. The major problems are the size and, as with the bagpipes, a single blow in the main body of the instrument and it’s ruined.
Pianos and other keyboards deserve special mention. Generally stationary, the only time these take to the battlefield is when the cause is enough for the equipment to be hauled by horses, generally during a time of battle. A skilled pianist is capable of choosing many of the aspects of the damage of the instrument, from area of effect to type of damage. It is the versatility of the instrument that makes it so useful.
The Pipe Organ is more powerful yet, and even bulkier than the piano. Generally only brought to the field in a time of war, the effects of a large enough pipe organ can be felt across the entire field.