UPDATE: Well, the free download is no longer available, but you can hear Hilary performing some of the tunes found in the sonatas, as well as some Bach, courtesy of NPR's Tiny Desk Concerts.
Q2 is commemorating Ives' birthday by offering a free download - today only! - of Hilary Hahn and Valentina Lisitsa's recording of Ives' Violin Sonata No. 4 'Children's Day at Camp Meeting. Great performance.