In the second example a SOM is used to analyze gamelan music. Gamelan orchestras originate in Indonesia and do not use the Western major and minor scales; they use two distinctive scales called slendro and pelog. Furthermore, gamelan music is played on non-Western instruments. Most instruments are idiophones such as gongs and metallophones, which, in contrast to Western instruments, often do not show harmonic overtone spectra. The tunings of these instruments and, consequently, the intervals of their scales are distinctive and differ slightly between orchestras. It is supposed that the interplay of the tuning and the particular inharmonic overtone spectra is crucial for the characteristic sound of Gamelan music [5].

This interplay can be explored with another [to do] interactive online demo.

In this application a recording of a gamelan tune is played, composed using the slendro scale. Its tuning can be manipulated by moving the four sliders, allowing everyone to design the tuning they prefer. One can also find buttons for directly switching to gamelan or traditional Western tunings.

People who have experimented with the online demo and listened to different tunings of the musical piece often stated they perceived the original slendro scale as the most authentic and appropriate, while Western scales, e.g. the major scale, were described as sounding rather pale or childish. This is striking, as most of the listeners had no or little experience with gamelan music, but were educated with Western music and its own scales and tunings. It cannot be assumed, however, that the interplay between scale tuning and overtone spectra is more important than musical education, as this interplay is also important in Western music. Different spectra may require different scales and tunings.

Perhaps AI, as a neutral, unbiased analysis tool, could help find a suitable ratio of tuning and spectrum for the characteristic sound of gamelan music. In the last few decades some gamelan orchestras have been founded in Germany. Can AI reveal a difference in the approach Western musicians have to Gamelan music? To answer this question two different SOMs were trained and can be explored in an [to do] interactive online demo.

Both maps are based on the same set of training data. The color indicates a specific orchestra while the shape of the markers depicts the orchestra's origin, either Indonesia [diamonds] or Germany [circles].

The SOM on the right was trained by focussing on the overtone spectra. Defined regions for every single orchestra can be easily recognized. These individual spectra may be the reason why every orchestra uses slightly different tunings. Furthermore, no systematical differences between German and Indonesian orchestras can be detected. For this reason it is more likely that different tunings are used due to different instrument spectra than due to the cultural roots of the musicians.

The SOM on the left was trained using various timbral features introduced in [to do] Section 3.1. How these features fluctuated during musical performances was analyzed. As these fluctuations must be related to dynamics, expression and articulation, the different component planes reveal that the Indonesian orchestras performed in a more balanced way, while the German orchestras tended to have strong fluctuations or no fluctuations at all. Nevertheless, it remains unclear if this is due to musical structure and composition or if the fluctuations arise, rather, from musical expression and dynamics.

In either case AI did detect differences between Indonesian and German musicians in gamelan performances and, yet, the overtone spectra and tuning were individual to every orchestra, independent of its origin. Further research, and maybe more AI models, is needed to systematically describe the interplay of scales, tuning and overtone spectra.