Modal Shift of Tonic and Evolution of Musical Scales

Abstract

The evolution of melodic music in India can be attributed to the principles of modal shift of tonic, also known as Graha Bedha in Indian music. This later led to a gradual evolution and conception of melodic scales based on the theories of consonance and dissonance. The classical music system which is prevalent in South India popularly known as carnatic music uses 12 semitones within an octave, as in Western classical music. The seven syllables in the solfa system are denoted as S, R, G, M, P, D, and N. The notes S and P are fixed in frequency intervals while the notes R,G,M, D and N can have three variations, some of which overlap as follows: R1 (minor second), R2 = G2 (major second), R3 = G2 (minor third), G3 (major third), D1 (minor sixth), D2 = N1 (major sixth), D3 = N2 (minor seventh), N3 (major seventh). By arranging each of the notes in ascending and descending order, 72 fundamental melodic scales have been derived which is the edifice on which the music of south India has evolved. The principles of modal shift of tonic when applied to these 72 scales yield different derived scales excluding some notes, or using the notes in a convoluted fashion. This paper presents new fundamental melody scales for the first time, by using both perfect fourth (M1) and the augmented fourth (M2) in the same fundamental melody scale. In addition to this it also presents some observations on the newly derived scales, which concur with the theories of consonance and dissonance, thus indicating the melodic potential of the newly derived scales. The melodic characteristics of these scales have been explained based on psycho-acoustic principles.

Keywords: Melodic scales, Consonance, Dissonance, Modal shift of tonic, Psycho-acoustics, Music cognition