A little over a year ago, tenor Ben Heppner had to shorten two recitals when he experiences vocal problems. “Ever since, the burly Canadian tenor has had to contend not just with demands of the music at hand, but with the public memory of those unfortunate, exceptional evenings. Two wretched nights in a 17-year international career is not much, but it’s enough to sharpen everyone’s ears for the next sign of trouble.”