Bulgarian folk songs are sung in a very special type of voice which I have not heard elsewhere. The singers have a normal voice when talking, but change when singing. Can you tell me more about it? Does it have a name, how is it achieved, is it used in other musical traditions?
This video of an interview with a singer has a very good example:
From 0:10 to 0:30, there is a standard recording of a song, as would be heard on an album. You can hear the voice in its most common form.
From 1:50 to 2:42, she's singing live in the TV studio. She's still using this voice, and although it's a bit different than the first recording, you can hear it's something she does, not a special effect added later.
And then the interview starts, and she talks with a normal voice, different from the one she uses for singing. From about 3:30 on, you can hear her talking. They are also using her recording as a background, so the contrast is very noticeable.