Marten Jansson Missa Popularis. As the name suggests, the “Missa Popularis” has its musical roots in folk music.This becomes clear in the very first bars of the Kyrie, where the violin plays amelody in the style of a Swedish folk tune above a bass ostinato. The musical charm of the Mass derives from the combination of choir [SSA(TB)] and string quartet.The choral parts enable performances by female choir or mixed choir. In the latter case the string quartet is reinforced by a double bass.