Kolkata: 700032, INDIA
Rekhi Centre of Excellence for the Science of Happiness
IIT Kharagpur, 721301, INDIA
Popular version of paper 4aMUa3
Presented Thursday morning, December 10, 2020
179th ASA Meeting, Acoustics Virtually Everywhere
The Indian classical music (ICM) system is based on the note system which consists of 12 notes, each having a definite frequency. The main feature of this music form is the existence of ‘Ragas’, which are unique, having a definite combination of these 12 notes, though the presence of 12 notes is not essential in each of the Raga; some can have only 5 notes which are usually called ‘pentatonic Ragas or scales’. Each Raga evokes not a particular emotion (rasa) but a superposition of different emotional states such as joy, sadness, anger, disgust, fear etc. A mere change in the single frequency of a Raga clip changes it to another Raga and also the associated emotional states change along with it. In this work, for the first time, we envisage to study how the emotion perception in listeners’ change when there is an alteration of a single note in a pentatonic Raga and also when a particular note(s) is replaced by its flat/sharp counterpart. Robust nonlinear signal processing methods have been utilized to quantify the acoustical signal as well as the brain arousal response corresponding to the two pair of Ragas taken for our study.
The two pair of ragas chosen for our study:
Raga Durga- sa re ma pa dha sa
Raga Gunkali– sa RE ma pa DHA sa
The notes ‘re’ and ‘dha’ of Durga is changed to their respective sharp/flat counterparts which change Raga Durga to Raga Gunkali.
Raga Durga- sa re ma pa dha sa
Raga Bhupali- sa re ga pa dha sa
The note ‘ma’ in Raga Durga, when changed to ‘ga’, makes the Raga Bhupali
Human Response Analysis-
A human response study was done with 50 subjects who were provided with an emotion chart of the basic 4 emotions, and were asked to mark the clips with their perceived emotional arousal.
The radar plots for the human response analysis:
(Fig. 1 a-b) Pair 1
(Fig. 1 c-d) Pair 2
It is seen that the change of a single note manifests in a complete change in emotional appraisal at the perceptual level of the listeners. In the next section, EEG response of 10 participants (who were made to listen to these raga clips) has been studied using nonlinear multifractal tools. Multifractality is an indirect measure of the inherent signal complexity present in the highly non-stationary EEG fluctuations.
The following figures give the averaged multifractality corresponding to the frontal and temporal lobes in alpha and theta EEG frequency range for the two pair of raga clips. P1…P5 represents the different phrases (note sequences) in which the main changes between the two ragas have been done.
(Fig. 2 a-b) Pair 1
(Fig. 2 c-d) Pair 2
For the first pair, alpha and theta power decreases considerably in the frontal lobe, while in temporal lobes, phrase specific arousal is seen. For the second pair, the arousal is very much specific to the phrases. This can be attributed to the fact that the human response data showed the emotional arousal in second pair is not strongly opposite to each other, but a mixed response is obtained. For the first time, a scientific analysis on how the acoustic, perceptual and neural features change when the emotional appraisal is changed due to the change of a single frequency in a particular Raga is reported in the context of Indian Classical Music