One other thing. You start the depreciation clock when you place the instrument "in service" in business. If you bought the instrument as a student in 2013, and became a professional musician in 2015, then you would start depreciating the instrument by listing is as an asset on your 2015 tax return. The basis for depreciation at that time would be whichever is lower -- your original cost, or the fair market value at that time. You would still need to file at least one amended return, depending on when you placed the instrument in service for business, and you still have to consider the issues around recapture whether it will hold its value.
