Play Instrument (sage ability)
Play instrument is an amateur-status sage ability, in the study of Accompaniment, describing the character's skill in playing a traditional instrument, typically a mandolin, lute, violin, drum, horn or the pipes. This is considered to be the musician's first instrument, so his or her master should have taught an instrument that is lightweight and easy to maintain and play. Only one instrument may be chosen.
Through the musician's training and from elsewhere, it's understood that the musician has acquired a bevy of songs — ballads and songs for drinking, working, love, sadness — and that he or she is able to perform these competently. Naturally, the musician likely plays these often, with music becoming familiar around the party's camp on a near-daily basis.
However, once a month, or after a period of at least 30 days, the musician may give a performance, presenting a new song that's been learned and practiced — and the pleasure received from listening to this song gives the audience a feeling of well-being, confidence and clarity of mind. This translates into a +5% experience bonus that lasts for twenty-four hours. Since the musician can decide precisely when to give this performance, presumably this can be prior to an expected battle or in the hours before entering a dungeon. The performance must last half an hour and can be given while waiting on the battlefield (when martial strains would be expected) or — if practical for the instrument being played — while approaching the dungeon or enemy's lair.
A performance may be given in any new venue the character enters, for the patrons there won't have heard the musician play before — thus the "once a month" requirement is met for each stranger. The party may not receive any special benefit from most of these nights, but the new audience will. Importantly, the audience must be ready and appreciative of the would-be performer! A performance cannot be forced on a crowd who happens to be present, but are not interested in listening. An introduction by the proprietor is therefore necessary for a performance to take place.
From the above, it can be extrapolated that if the player characters seek out and visit venues where qualified non-player musicians are performing, the 5% bonus can yet be obtained. This is true. Players are encouraged, when in a city, to find such places and enjoy the pleasantries of being entertained in a manner that provides a practical game benefit — remembering that this can only be gained once per month from any specific performer, regardless of the skills they present.
By seeking out population centers, the players can amuse themselves and enjoy the experience boost, while feeling part of the artistic scene. Encountering a musician or a troupe at random while travelling becomes a reason to be excited, with real game benefits to boot.
Music as Accompaniment
Ordinarily, there are many kinds of performance that provide the 5% experience bonus: a dancer, an acrobat, a poet or an actor may each provide their own form of entertainment ... but when each is done while accompanied by music, the overall benefit of both is +8% rather than the lesser amount. There is an overall 1 in 4 chance that any musician giving a public performance will be accompanied by another performer of some kind; and player characters with musician skill may enjoy hiring or finding an associate for the general benefit it gives their audience.
If two or more musicians play together, the overall benefit is +6% rather than +8.
Not every audience is impressed with an amateur, or even an authority-status performer. Members of the higher classes have heard every song an ordinary musician can play. Therefore, audiences can be rated on a scale of 1 to 100, depending on how jaded they are ... in which case, the knowledge of the performer must outdo the expectations of the audience, in order for the benefit to be received. This is easy to do in a small venue like an inn or a tavern, but much harder to do elsewhere. As a rule of thumb, allow that for every experience level of the audience, a knowledge level of 6 points are needed to impress. To affect a 12th level lord, then, the character would need 72 knowledge points as a musician or accompanist.