|Augmented reality is more than just superimposing VR over the physical world visually. It is more than sounds for your ears only. Fundamentally it is the complete fusion of computer mediated synthetic reality with the physical reality around us, to the point that the two realities become one.
To this end, there are an impressive number of senses and positional elements to interface with.
Resource List: Visual AR Development
Visual augmented reality elements are amongst the simplest AR elements to integrate into the physical environment. That said, tracking and adjusting for a continually changing user viewpoint, without it becoming obvious that the data is superimposed from VR, is a major undertaking.
Combined with the problem of occluding virtual data that physical objects pass in front of, there is enough challenge to keep developers occupied for a long time to come.
Resource List: Auditory AR Development
Auditory AR elements are hands down the easiest to integrate into the physical world. As you pass a given location, or as you approach it, a sound plays. This form of AR has been with us for many years.
Things get a little more complex when AR sound is integrated with other methods such as AR visual scenes but not much more complicated, at all.