Finland hasn't figured very prominently in the last decade's explosion of interest in "world music," but maybe Varttina can change that. At home the nine-piece group has spearheaded a revival of popular interest in folk music; its 1991 Oi Dai was the first folk album to go gold in Finland in 20 years. The group is trying to repeat the trick abroad on its first complete North American tour. The core of Varttina's sound is its four female vocalists: they sing exclusively in Finnish, a rich-sounding language replete with rolling Rs and nasal vowel sounds that bears little resemblance to other European tongues (most are in the Indo-European family, while Finnish is more closely related to Basque and Mongolian). This emphasis allows American listeners to concentrate on the beauty of their close, bright harmonies, without being distracted by their archaic lyrics about the pros and cons of marriage. Varttina's five musicians play accordion, fiddle, and a host of other stringed instruments. On their new album, Seleniko, the accompaniment sounds almost Celtic--but their embellishments are more melodic and less droning than most Celtic folk music, and where many Irish and Scottish bands get bogged down by bland crossover-pop moves, Varttina's acoustic purity only enhances their exuberant, life-affirming music. Sunday, 5 and 8 PM, Old Town School of Folk Music, 909 W. Armitage; 525-7793.