On hearing that “Nostalgic Synchronic” is composer Dan Trueman’s beautiful, surprising and innovative set of eight etudes for “prepared digital piano,” you may wonder what such an instrument could be. Just as John Cage used rubber, metal and plastic to alter the sound of a physical piano, Trueman uses the resources of the electronic keyboard to introduce variations to what is still a recognizable piano sonority. Pitches get bendy, notes echo and fade at unpredictable lengths, and individual notes take on odd colors — and through it all, the familiar strains of the piano continues unabated. If the sounds themselves are striking, Trueman’s writing is no less so: a mixture of moody reverie and vigorous virtuosity, with overtones of Bach, Chopin and Nancarrow thrown into the mix.