The folksong collectors Bartok (Hungary) and Plicka (Czechoslovakia) notated the perceived interval deviations with a plus or minus sign (+,-). Older folksong collectors had notated all the intervals in the system of semitones, not observing the finer modifications of intervals. This first gained currency from the phongraph and tape recordings of folk music from various lands....From folksong I learned to perceive melodic intervals a little smaller or greater than those of the semitone-system....In my youth it often happened that the folk singers, who during the intermissions of dance festivals sang songs of "their kind," deviating from the semitone system, demanded that the first violinist of the Wisowitzer Kapelle play "their" melody just as they sang it. Once a tempermental singer threatened to strike the double-bass player with a beer mug if he didn't "play along" with the song, exactly as he sang it.
Mein Weg zur Viertel- und Sechsteltonmusik (1971) Düsseldorf: Verlag der Gesellschaft zur Förderung der systematische Musikwissenschaft, 12, 14; translated by and printed in Modernism and Music: An Anthology of Sources(2004) by Daniel Albright ISBN 0226012670 .