IPO method

Intonation grammar developed at the Institute for Perception Research in Eindhoven ('t Hart et al. 1990) which reduced all pitch movements in Dutch to an inventory of ten standard pitch movements: five types of rises (indicated by numbers 1-5) and five types of falls (indicated by letters A-E). These movements cannot be placed after each other at random: the IPO grammar determines which movements can be combined. This grammar distinguishes a basis configuration (the only obligatory part), which can be preceded by prefix configurations, and followed by the suffix 2 (i.e. the final rise). The basis configuration consists of one or two pitch movements: 1A (the pointed hat contour), 4A, 3C, 1E, 1 and 2. These movements are superposed on the declination line: there is a general downward trend in pitch during the utterance. In between the pitch movements, pitch lowers on the low declination line or, after a rise, on the high declination line. The IPO method has also been used to describe other languages, apart from Dutch, but not without some adjustments. For English, e.g., three declination lines are assumed in order to describe the greater variety of pitch movements.

Link
Utrecht Lexicon of Linguistics