It's at best misleading to describe the Carpenters as a "singing duo". Karen did most of the singing, while her brother Richard (defying gender stereotypes) was a real multi–tasker. To quote Wikipedia, "He has had numerous roles including record producer, arranger, pianist, keyboardist, lyricist, and composer, as well as joining with Karen on harmony vocals."
Aha, I hear you say, there you go: "joining with Karen on harmony vocals." But if you think of any Carpenters track (don't pretend you can't) I'll bet a pound to your penny that it's Karen's voice you hear, not Richard's.
Except that I'm not betting, because you'd say you could hear Richard's voice, even though you couldn't.
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