Stéphanie Weisser

Generating structured music for bagana using quality metrics based on Markov models

We combine machine learning and optimization techniques to generate music.We study novel ways of using a Markov model to construct an objective function.A Markov model is combined with repetitive and cyclic aspects of a music template.We show the effectiveness of the methods on Ethiopian bagana songs. In this research, a system is built that generates bagana music, a traditional lyre from Ethiopia, based on a first order Markov model. Due to the size of many datasets it is often only possible to get rich and reliable statistics for low order models, yet these do not handle structure very well and their output is often very repetitive. A first contribution of this paper is to propose a method that allows the enforcement of structure and repetition within music, thus handling long term coherence with a first order model. The second goal of this research is to explain and propose different ways in which low order Markov models can be used to build quality assessment metrics for an optimization algorithm. These are then implemented in a variable neighborhood search algorithm that generates bagana music. The results are examined and thoroughly evaluated.

Antipattern Discovery in Ethiopian Bagana Songs

This paper develops and applies sequential pattern mining to a corpus of songs for the bagana, a large lyre played in Ethiopia. An important aspect of this repertoire is the unique availability of rare motifs that have been used by a master bagana teacher in Ethiopia. The method is applied to find antipatterns: patterns that are surprisingly rare in a corpus of bagana songs. In contrast to previous work, this is performed without an explicit set of background pieces. The results of this study show that data mining methods can reveal with high significance these antipatterns of interest based on the computational analysis of a small corpus of bagana songs.

Emotion and music: The Ethiopian lyre bagana

The bagana is a paraliturgical lyre played by the Christian Amhara of Ethiopia. It is used to perform spiritual music. Bagana is an intimate instrument, accompanied by the singing voice only. It has a special role in Christian Amhara music, as its myth of origin closely connects it to God, the biblical King David and King Menelik I. It is reputed to be very powerful and its performances arouse intense reactions in both players and listeners. Some of these reactions were observed directly (immediate calming, tears, overwhelmed faces). Inner reactions to bagana were investigated by means of 108 statements collected from 32 participants (from virtuoso players to simple listeners) during interviews or discussion. Statements were classified by using the Strong Experiences related to Music (SEM) descriptive system (Gabrielsson & Lindström Wik, 2003). Results show that the inner reactions bagana elicits are varied (statements fall into six of the seven categories of the SEM descriptive system) but a majority of the statements can be classified into the Feelings/Emotions (5) and Existential and Transcendental (6) categories. The least commonly admitted reactions fall into the Physical Reactions and Behaviours (2) and the Perception (3) categories. These results are discussed in detail and confronted with the direct observations. The utility and difficulties of the SEM descriptive system in ethnomusicological contexts are also discussed.

Etude ethnomusicologique du bagana, lyre d'Ethiopie

Cette these decrit et analyse les caracteristiques ethnologiques, musicales et acoustiques de la lyre bagana des Amhara d’Ethiopie. L’etude des donnees ethnologiques montre que le bagana incarne de nombreuses valeurs de la societe traditionnelle amhara. Instrument considere comme un don de Dieu et qui fut joue par des rois, le bagana est sacre. C’est un instrument intime, dont le jeu (toujours en solo ou accompagne seulement de la voix) est considere comme un acte de priere ou une meditation a caractere religieux. Le musicien ne se donne pas a voir, ni par une dimension spectaculaire de sa performance, ni par une dimension phatique.L’analyse des accords utilises dans le repertoire du bagana montre que cet instrument est essentiellement accorde selon deux echelles modales pentatoniques, tezeta et anchihoye. L’organisation temporelle des chants de bagana est fondee sur des pulsations discretes tres rapides. La pulsation apparente se compose d’un multiple de cette pulsation discrete qui change en fonction du motif joue, ce qui cree une sensation de rythme libre ou de rubato. Les chants de bagana sont fondes au niveau melodique sur des unites qui se composent de paires de notes. L’analyse musicale du repertoire du bagana montre que celui-ci est fonde sur la repetition variee d’un ostinato musical assez court couple a des paroles qui changent sans se repeter (a l’exception du refrain) selon les lois de la poesie amharique orale traditionnelle. Les procedes de variations mis en œuvre sont en general assez subtils car ils doivent preserver la sensation de repetition tout en apportant des elements nouveaux. L’etude des proprietes acoustiques du bagana permet de determiner que celle-ci produit des sons tres graves (jusqu’au sol 1). Le dispositif chevalet large-obstacles modifie tous les parametres du son. L’analyse de la facture traditionnelle montre que l’instrument est concu pour produire un son gresillant, long et intense sans avoir recours a une caisse de resonance volumineuse. Le bagana est un instrument puissant, qui permet l’etablissement d’une relation directe avec des entites surnaturelles via une transe legere. La voix et l’instrument sont dans un rapport de fusion et de renforcement mutuel. Les modes phonatoires utilises sont « breathy » et « harsh ». La presence de la voix agit comme un guide perceptif, qui intervertit le rapport fond-forme dans la perception de l’instrument.

Pattern and Antipattern Discovery in Ethiopian Bagana Songs

Pattern discovery is an essential computational music analysis method for revealing intra-opus repetition and inter-opus recurrence. This chapter applies pattern discovery to a corpus of songs for the bagana, a large lyre played in Ethiopia. An important and unique aspect of this repertoire is that frequent and rare motifs have been explicitly identified and used by a master bagana teacher in Ethiopia. A new theorem for pruning of statistically under-represented patterns from the search space is used within an efficient pattern discovery algorithm. The results of the chapter show that over- and under-represented patterns can be discovered in a corpus of bagana songs, and that the method can reveal with high significance the known bagana motifs of interest.

Acoustic characteristics of Ekonda scrapers

This paper describes some acoustic characteristics of a musical instrument played with the complex vocal polyphonies of the Ekonda of the Congo. The complexity of these songs and the remarkable pitch accuracy of their intonation are striking given that there is no tuning fork or fixed pitch instrument which can account for the pitch stability. Ekonda scrapers are required to accompany the polyphonies. An acoustic study of these idiophones was made to understand their contributions to the songs. The scrapers are made in a hollow piece of a palm tree branch. The instrument is played by rubbing a piece of hard wood upon splits made on the piece of palm tree. In addition to the friction noise due to the rubbing of the piece of hard wood, there are some very distinct resonances which can be identified. An important observation is that there is always a very intense resonance at the frequency of the musical scales tonic. The relation between the pitch of the tonic and the frequency of the scrapers resonances which act as a tuning fork are detailed.

The acoustics of the bagana

The bagana is a big Ethiopian lyre with ten strings. The instrument is found in the area of the Amhara, the culturally dominant tribe of Ethiopia. It is an intimate instrument, played only with the voice, for prayer and meditation. It can be tuned in two pentatonic scales, and can be plucked with the fingers, string by string or with a plectrum, all strings together. The box of the bagana is made of wood covered with leather, and the strings are made of gut. They are very thick and between them and the bridge, there are ten buzzers. Therefore, the bagana produces a very deep and buzzing sound. The paper will analyze the acoustical function of several parts of this instrument, e.g., the sound box and its crosslike hole at the back. The influence of the buzzers on the fundamental frequency, the spectrum, the duration, and the intensity of the signal will be closely examined. The role of the five unused strings (the ‘‘rest’’ strings) will also be examined.