Heard on the Nov. 14 Multe Music podcast "November Blues" out of Northfield, Minn. ... according to program host Ruth Marie Sylte, some halftones are known as "blå tonar" in traditional music ... mostly Norwegian (?) but a couple of tracks by Swedish and Danish musicians. Most accessible example: "Blå tonar frå Lom" by Hans W. Brimi & Pernille Anker on the Nordisk Sang compilation disc.
Most of these sound modal to my ear, but some interesting influence of African American music - a lot of jazz and some blues - on some of the groups she features. Not to be missed: "Forårslængslens Bluespolsk" featuring Kristine Heebøl (and I'm sure I hear Nikolaj Busk on keyboard) from the Trio Mio CD.