A decent, simple music puzzle game that has a fair bit of complexity in later levels but can take a little bit of time to ramp.
Each "Act" features a different piece of music which you create by sending a stream of music across different bars. Each set of bars will be a different part (melody, bass, secondary, etc) which combine to create the piece of music for that act. This is done using a varying set of tools (directional/rejection, portals, speed up/slow down, etc) and challenges (colors, splitting streams, etc) in order to meet the requirements for each level. It should be noted that while this is a music game, it's NOT a rhythm game.
While there's no demo, you can find the first 2 (or 3? I can't recall) Acts on the developer's website: http://www.cipherprime.com/games/auditorium
which introduces the core concepts. It's how I was first exposed to it years before it came out on Steam.
This isn't a game that I'd recommend sitting down and cranking through - you'll knock out a few levels, and then move on to something else. It's not terribly difficult, but makes for an excellent, relaxing palete cleanser. Think "tablet game designed before tablet games were a thing."