Traditional Albanian polyphonic music can be divided into two major stylistic groups as performed by the Ghegs of northern Albania and the Tosks and Labs living in the southern part of the country. The term iso is related to the ison of Byzantine church music and refers to the drone accompanying polyphonic singing. The drone is performed in two ways: among the Tosks, it is always continuous and sung on the syllable 'e', using staggered breathing, while among the Labs, the drone is sometimes sung as a rhythmic tone, performed to the text of the song. Rendered mainly by male singers, the music traditionally accompanies a wide range of social events, such as weddings, funerals, harvest feasts, religious celebrations and festivals such as the well-known Albanian folk festival in Gjirokastra.