  In North Indian Classical music, each raga has been traditionally associated
with a performance time, which supposedly maximizes its aesthetic and emotional
effects on the listener. The objective of this work was to investigate the
structural basis, if any, for the association of ragas with different times of
the 24-hour span. The tonnetz framework has been used to analyze the pitch sets
of 65 North Indian Classical ragas, and structural similarities have been
observed between ragas associated with (1) times of transition between day and
night, i.e., dawn and dusk, and (2) times between these transitions. These
findings could provide some insight into the scientific basis of the age-old
raga-time relation, and their effects on the perception of the listener.
