"The blowing of these flutes within the appropriate ritual context is to invoke the presence of the spirits with which they are associated, to make the powers associated with these spirits accessible to humans. The flutes are made, owned, played and kept secret by adult men. Women and children are forbidden to see the flutes and are told that the cries of the flutes are the voices of actual spirits." These are probably my two favourite albums that I have. Vol. 1 has four longer pieces. Vol. 2 features 12 shorter pieces on a wider variety of flutes. Excerpts can be heard here, and here. Recorded in 1974. Liner notes included.
More of this music can be heard on the equally good Music Of Oceania, Papua New Guinea: The Middle Sepik and The Iatmul Of Papua New Guinea. A film which has a lot of this music can be bought here Namekas: Music In Lake Chambri/Preview, a beautiful film filled shots of village life and the surrounding landscape, in one sequence a man uses a living beetle for an instrument, singing into it's buzzing wings.