Looking for suitable µC to process Audiosignals

Hi there.
I´m planning to build some eletronic music instrument for which i want 
to use an µC.

My first prototype should be very simple in function:

My "instrument" has 12 touchsensitive swichtes and each of them should 
play a predefined sound.
It has to be possible to play different sounds at once.

I thought of some Atmel µC, because i´m quite experienced with these.
I don´t know much of creating a file system, so the µC should support 
FAT16 and the .raw audio format.

Do you have any ideas for me?

Thanks, regards,
Mosha