Chicago’s acclaimed vocal ensemble Chicago a cappella spotlighted songwriting and performing duos on their April 2019 program, “Dynamic Duos: The Greatest Musical Partnerships.” Veteran pop arranger Paul Langford provided music direction and new arrangements of songs by Elton John & Bernie Taupin, the Carpenters, Hall & Oates, Simon & Garfunkel, and more. The ten professional vocalists of Chicago a cappella also presented works from opera, operetta, musical theater, as well as familiar pop songs.