Although I long to hear Adler Fellow and Metropolitan Opera National Auditions winner Nadine Sierra in her Schwabacher Debut Recital, duty demands that I take in the recital of Sandrine Piau, who makes her long-overdue Bay Area recital debut in Berkeley two hours earlier. Those who have been waiting to hear this marvelous soprano live will finally get their wish. Expect Piau’s vocal beauty, unassuming delivery, and unassailable technique to make a special experience of her chosen song repertory.