Sweet song from a couple including large contralto (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

DUET (a piece of music for two performers = song from a couple), including L (abbreviation for large) + C (abbreviation for the contralto singing voice, though it’s now more often represented as A for the shorter form “alto”). As in “dulcet tones” = sweet-sounding.