Gillian Welch explains that Emmylou Harrisand Alison Krauss took delight in making her sing the highest part in their trio, "Didn't Leave Nobody but the Baby", when both Harris and Krauss have higher-register voices.
Harris sang the bass part on the song, which is unusual for the singer, who is well known for her role as the "angel" vocalist in duets and backing vocals with other artists.
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http://en.wikipedia.org/wiki/Down_from_the_Mountain
http://en.wikipedia.org/wiki/O_Brother,_Where_Art_Thou%3F_(soundtrack)
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