This song, from Chandramukhi, is set in F minor (4 kattai). Sudhadhanyasi in F minor is F G# A# C D# F (or) Sa Ga2 Ma1 Pa Ni2 Sa, whereas the scale of this song is F G# A# C E F (or) Sa Ga2 Ma1 Pa Ni3 Sa - Just a half note difference. This scale is the same as "Sindhiya venmani" song in a Vijayakanth film. I read somewhere that this scale is the Srothaswini raga.
In the later half of the first interlude (after the thom thom thom portion), he does a tonal shift and changes the shruthi to E major (3 kattai) in Pantuvarali raagam. i.e., The Ni3 now becomes the Sa. The scale of this is E F G# A# B C D# E (or) Sa Ri1 Ga3 Ma2 P Dha1 Ni3 Sa. Then in the 1st charanam he again goes back to the original scale in F minor (4 kattai) and stays there in the second interlude too. This second interlude, with all those trumpets and strings, has more of sudhadhanyasi shades, with an occassional Ri2 popping up.
In the second charanam, the scale shifts to Hindolam raagam in C minor (1 kattai). The scale of hindolam is C D# F G# A# C (or) Sa Ga1 Ma1 Dha1 Ni2 Sa. It again goes back to F minor (4 kattai) during the pallavi after the stanza.
If you see compare the scales of the different raagams and the corresponding tonal shifts (shruthibedham), you can see that many of the notes (absolute notes) are the same, but are played in a different scale / shruthi. Here is a table comparing the various notes.
(in 4 kattai)
|Ni||Sa ||Ga||Ma ||Pa ||Ni ||Sa ||Ga ||... |
(in 3 kattai)
|Sa||Ri ||Ga ||Ma ||Pa ||Dha ||Ni ||Sa ||Ri||Ga ||... |
(in 1 kattai)
|Ma ||Dha ||Ni ||Sa ||Ga ||Ma ||Dha ||... |
|Western Notes ||E||F ||F# ||G ||G# ||A ||A# ||B ||C ||C#||D ||D# ||E ||F ||F# ||G ||G# ||... |
It is a wonderful composition and looks like he has followed IR's footsteps with respect to the tonal shifts (shruthibedham). One difficult thing in such a composition is the shruthi of the mridangam should also be changed as the shruthi changes. I don't think Vidyasagar has done that here. But IR has done that and is easily identifiyable in the song Vaidehi Raman.
On the whole this is a very good composition and suits the climax situation very well. It creates an anxiety of what would happen next. The singers Binny and Tippu have done full justice to the song. It was a pleasant surprise to hear Tippu in a classical song.