Well, I am not sure about is this is the right StackExchange site to ask this, but since can accept question about Software law, i think it's almost on topic here.
If I use creative commons music for non commercial usage in my project, it's fine if my final product is freeware.
But, what if it becomes ad-supported? It's considered commercial usage? And, if I do a paid ad-free version, this is commercial usage, i think.
Example: using this music as bgm in a game
Remember, there are different types of Creative Commons licences. If you pick music that does not have the NonCommercial condition, you don't need to worry about whether your software is free, ad-supported or paid-for (but do remember to check what other conditions apply, such as Attribution and NoDerivs).
I'm not a lawyer, but if you're making money, either directly from sales, or indirectly from selling adverts, then I would consider that commercial.
For example, the human-readable page of the Attribution-NonCommercial licence says:
Noncommercial — You may not use this work for commercial purposes.
The full legal code says:
You may not exercise any of the rights granted to You in Section 3 above in any manner that is primarily intended for or directed toward commercial advantage or private monetary compensation.
You'll get "private monetary compensation" from adverts.
Edit: so the added example is Attribution Noncommercial (3.0), which means you cannot just take it and use it in commercial software. However, Creative Commons licences are not exclusive:
Waiver — Any of the above conditions can be waived if you get permission from the copyright holder.
So you can still go and ask the creator (the copyright holder) directly for permission to use it how you want, and if you agree terms (free use, in return for something (money or credit)) then the CC licence no longer applies.
The best suggestion for the song you linked that I can give is that you talk with the original author about what you want to do and ask for permission. In case the license would limit the type of use you look forward to (which I assume but IANAL), the original author still can give you permission to compile the songs data into the executable binary of your game.
