Not too many singers have performed the lead role in Cavalleria Rusticana, toured as a Rae-lette with Ray Charles and sung with and been mentored by Von Freeman. But for Chicago jazz (and gospel and classical) singer Tammy McCann, those experiences have proven to be mere stepping stones in a career that has people buzzing about her in New York as well as the Windy City. Having recorded an album with the much-admired pianist-arranger Laurence Hobgood at the helm, she is poised to turn that buzz into a roar.