Southern California siblings Karen and Richard Carpenter were the picture-perfect radio-friendly '70s pop duo. And by and large, their recordings were marvels of lush soft rock, ribboned with muted horns and harps. But beneath the luminous surface, Karen's lilting alto invested even hopeful songs with melancholy, adding aching loneliness to “(They Long to Be) Close to You,” that paean to infatuation. Though the pair were hampered by personal demons, their music maintains an easygoing sweetness that made tunes like “Sing” and “Rainy Days and Mondays” sing-along favorites.