This music may be performed with any sound source (instruments, human voice, any kind of object, generators, etc.) suitable for producing the pitch of one of the four voices with a differentiation required by the piece.The four pitches are to be read in the treble clef, and only in the given register.Ali the sound sources may be modulated electronically. ln case of any kind of modulation the proportion of the modulated/ direct tone has to be selected in such a way that the constancy o...