The second week of Seattle Chamber Music Society’s Summer Festival wrapped up Friday night with half the performance being two-piano works, and the other half string octets, one of each being classical, one of each being 20th century, a good study in contrasts.

But first, the recital. This year, these free half-hours by one or two musicians introducing and performing their own choices have been some of the most absorbing performances of the evening, and Friday’s was no exception. It featured violinist Augustin Hadelich and pianist Orion Weiss in Stravinsky’s Divertimento for Violin and Piano, followed by Tchaikovsky’s Valse-Scherzo, Op. 34, not played here before.

On the face of it, this seems straightforward, but in his comments Hadelich announced this was a frivolous program, explaining that Stravinsky transcribed various works by Tchaikovsky to create a ballet, The Fairy’s Kiss, and in the process mischievously “Stravinskified” the Tchaikovsky. He and Weiss were about to perform first the Stravinsky version of one work, complete with “mistakes” where the performers get apparently out of sync before trying to recover, and then the original Tchaikovsky from which it was taken.

It was an extraordinary performance by both but particularly Hadelich who tossed off the difficult technical aspects with lightness and ease while maintaining the delight and fun in these works. Where else could we hear such a coupling, together with an explanation, and performed by two consummate artists who were completely in tune with each other and the music?