Parallel organum

Parallel organum is a style of composition based on plainsong or plainchant (e.g. Gregorian chanting). Organum is a form of polyphony developed in the Middle Ages in which at least one voice is added to the melody to enhance the harmony. An organum is considered "parallel" when the two or more voices are sung in perfect fifths, perfect fourths or octaves. The two voices may sometimes be in unison.<br><br>Early on it was found that singing in perfect intervals came naturally when the lower voices of adult males sang together with the higher register of adolescent boys. In this situation the upper voice was called the "vox principalis" and the lower voice the "vox organalis", which was usually sung at a perfect fourth below.<br>