A gifted jazz pianist and a singer with a limited range but a distinctive voice, he wrote mostly for grown-ups but reached his largest audience on “Schoolhouse Rock!”A gifted jazz pianist and a singer with a limited range but a distinctive voice, he wrote mostly for grown-ups but reached his largest audience on “Schoolhouse Rock!”Read MoreDeaths (Obituaries), Jazz, Music, Schoolhouse Rock! (TV Program), Frishberg, Dave