Chris Thile is compiling a laundry list of impressive musical exploits ranging from participation in the bands Nickel Creek and The Punch Brothers to hosting A Prairie Home Companion. A common thread in much of what he tackles in his musical life seems to be progressivism. In his collaborations, Thile’s choices for his mandolin are unexpected and unconventional. When you are a musician of Thile’s caliber, however, unexpected and unconventional make for the most compelling musical offerings. Case in point, his recent collaboration with pianist Brad Mehldau.