Software which reproduce melody

The task is create digital music processor or player. We need to play music notes with required sounds sample, this mean it must play with different instruments. We need freelancer which expirienced or have some skills in the required areas or at lease have an ideas how to solve this task. Format of notes sequence is up to you, it may be midi or some else or custom. The language of implementation is also free to choice, I suppose that most probably it will be C++ or any other or some mix of that. Let us know about your idea and expirience. What is your expirience useful to solve task? How do you suppose to solve this task? Also which language you choose and why? All suggestions are very appreciated. Thank you.