Swar Samvad.

The combination of two Swars produce a sound which is known as Dhwani.This Dhwani is sometimes soothing to ears and sometimes bad.If the Dhwani produced is Tuneless and feels bad to ears is known as Vivad.While the one in Sur is known as Samvad.For eg:Madhya Sa and Taar (higher octave)Sa combine together and give soothing Dhwani.The other two combination are Sa Pa and Sa Ma.These are known as Samvad.Combinations like Sa Re,Sa Ga,Sa Dh,Sa Ni, doesnot produce good dhwani and known as Vivad swars.