One aspect of Rahman's music that I truly find remarkable is his use of harmonies. His knowledge and application of chords is unmatched in the history of Indian music IMHO. He can use the same melodic line, apply a difference chordal sequence, and the melody sounds like a different melody. Now, that's genius.
One example, in the song "Tu Bin Bataye" from RDB, notice how the melody sounds when Madhrushree sings the "Meethi Lagi......." line. Then, listen to the same melodic line when Naresh Iyer enters the first time after the saxaphone music interlude. It's the same melody as Madhushree's line, but the chords are all together different. It almost sounds like a different melody. And in Naresh's line, Rahman adds the choral track which adds so much depth and dimension. A simple melody made even more beautiful by Rahman's harmonics and arrangements. There are many other exmples, too many to cite here.
