Future Music: While the Empire has been around for a very, very long time and as such has accumulated far more musical genres that I can reasonably describe, here are some notable ones – with staying power – in Imperial space:
Digital: This isn’t a parallel to our electronic music; it’s the native music of AIs and other digital sapiences. To most biosapient ears it sounds like a hideously cacophonic mixture of modem noise with a bank of packet sniffers all set for audio output, but that’s just because we don’t have the right ears to hear it properly.
There’s also a biosapient offshoot using theremin-like instruments which pull their input data from sampling the player’s neural activity, which makes it vitally important to pick your musicians’ emotional-conceptual phase spaces (“we need an ecstatic, a melancholic, and two tranquillaries to play this quarto”) to match the pieces you intend to perform.
Drinkin’ Music: (Yes, the actual word translates literally as “drinkin’ music”.) While this particular subgenre probably sounds most like Irish pub songs, from an Earth perspective, some of its best-known works are virtually impossible to perform when sober.
Emergent: A heavily improvisational musical school, and also the most danceable of the notable genres, “emergent” would sound to the Terran ear as something like a jazz-swing hybrid. It occupies the Empire’s “mainstream popular music” niche.
Fightin’ Music: (Yes, this one does too.) Heavy on the trumpets, bagpipes, percussion, and bombast. Really serious works in the genre include unconventional percussion instruments like spears-on-shields (after all, much of it was written to be performed on the battlefield), and modern examples may add firearms and small artillery pieces, and in one memorable example, the main armament of a Bellicose-class assault cruiser. (The Ethring Nautical Symphony actually owns one, surplussed out of the Capital Fleet; the piece in question is remarkably popular during the Armament Day celebrations.)
The combination of the drinkin’ and fightin’ music genres is… best left unmentioned.
Filk: Well, speculative fiction is one of their major literary genres, so what would you expect? (An outgrowth of Traditional, which see.)
Metatonal: The music of the augmented, metatonal makes use of elements, in audible range, timing, and differentiation between notes, that are impossible for the unaugmented ear to hear. Or music that is targeted at an audience of two species at three different pitch ranges, of which only the middle one is audible to both. Or – well, the more complexity you can cram into the music, and the more people you can please with the result despite their different perceptions, the closer you come to the real spirit of metatonalism, so they say.
Opera: While stylistically and dramatically similar to opera as we know it, Eldraeic opera includes elements of ballet, and is – in its higher forms – notorious for particularly involuted plots and extraordinary numbers of layers of symbolism. It’s also often performed in archaic languages, or archaic dialects, at least. In short: while still widely enjoyed, this is where Imperial high culture reaches its apotheosis.
Traditional: An outgrowth of the historical bardic tradition, this occupies what is effectively the “classical” music niche. While there is considerable variety within the genre, the typical examples are relatively lengthy ballads or similar works, with relatively subtle instrumental accompaniment. While not always presented, most also come with some form of visual accompaniment.