Role of Temporal Fine Structure and Envelope in Identifying Ragas: A Prospective Study for Temporal Based Raga Classifier

Abstract

Background and Aim: A raga is characterized by its distinctive melodic shape. The ability to perceive intricate melodic and pitch patterns depends on the Temporal Envelope (ENV) and Fine Structure (TFS). The present study aimed to understand the importance of temporal envelope and temporal fine structure cues in identifying ragas in Indian music. Methods: Twenty‏-‏one adult’s musicians were included in the study. In experiment 1, professional musicians were involved in a raga identification task using music chimaeras. In experiment 2, the chimaeras were subjected to acoustic analysis using the envelope difference index, to understand better how the ENV and TFS changed depending on how many frequency bands were used to create the chimaeras. The subjective impression of a new group of trained musicians was then compared to these results. Friedman’s test and Wilcoxon tests were carried out. Results: Results showed that both cues are crucial in a trade-off manner; when TFS are not significantly accessible, ENV aids in raga identification. It was reflected in experiment 1 as an increase in ENV scores and a decrease in TFS scores as the number of frequency bands increased. In experiment 2, the envelope difference index for ENV increases with a number of frequency bands, and it correlates with perceptual scores for ENV. Conclusion: The current study highlights the perceptual role of temporal cues in raga identification and directs future work for a temporal-based raga classifier. Keywords: Ragas; envelope; fine structure; Indian music; music information retrieval