Graha Bhedam in Carnatic music is the process (or result of the process) of shifting the Tonic note (śruti) to another note in the rāgam and arriving at a different rāgam.
Graha literally means position and Bhedam means change. Since the position of the śruti is changed (pitch of the drone), it is also sometimes called Swara Bhedam or Śruti Bhedam though Śruti Bhedam and Graha Bhedam have some technical differences.
A simple practical demonstration of Graha Bhedam can be taken up by playing the structure of a rāgam with the drone set to Sa (Shadjamam). Then if we keep playing the same keys/ notes, while shifting the drone to another note in the rāgam, to form the new śruti/ tonic note, the result is a different rāgam.
C as the base for Shankarabharanam is chosen for above illustration only for convenience, as Carnatic music does not enforce strict frequency/pitch structure. The Shadjamam (S) is fixed by the artist as per the vocal range or the instrument's tonic note. All the other swarams are relative to this Shadjamam, falling into a Geometric progression-like frequency pattern. This note is applicable to all tables that are illustrated further below in this page.
The 6th Graha Bhedam of Shankarabharanam has both Madhyamams (Ma) and no Panchamam (Pa) and hence will not be considered a valid Melakarta (ragam having all 7 swarams and only 1 of each). This is only a classification issue with respect to Melakarta, while this structure could be theoretically used well to create good music (probably needs an expert). Hindustani classical raga lalit has 2 Ma and no Pa, however it has different Ga and Ni than this structure
The gaps in the above table are for the missing swara positions in these ragams, which happens to be the Sharp / Flat notes in western music.
Graha Bhedam can be applied on most Melakarta rāgams to yield other Melakarta rāgams (16 of the 72 do not yield any valid Melakarta scale). When applying such modal shift of tonic note, some results are not valid Melakarta rāgams (rules of the definition of Melakarta are violated). Example scenarios are missing Panchamam (Pa) or two of particular note (Rishabham (Ri), Gandharam (Ga), Madhyamam (Ma), Dhaivatam (Da) or Nishadam (Ni)).
Graha bhedam can be applied to some of the janya rāgams to yield other janya rāgams. Unlike Melakarta rāgams, where strict rules are adhered to, in terms of which swaras can be chosen in a rāgam, janya rāgams do not have such rules. Hence, such modal shift of tonic note is valid on all swaras, but may not have been chosen as a rāgam, experimented, elaborated and composed. Hence they lead to theoretical rāgams, which have not yet been discovered (all combinations of notes exist, but no one has composed using a particular combination or experimented/ exposed to the world at large).
C as the base for Mohanam is chosen for above illustration only for convenience, as Carnatic music does not enforce strict frequency/note structure. The Shadjam (S) is fixed by the artist as per the vocal range or the instrument's tonic note. All the other swarams are relative to this Shadjam, falling into a Geometric progression-like frequency pattern. This note is applicable to all tables that are illustrated further below.
The gaps in the above table are for the missing swara positions in these ragams, which happens to be the Sharp and Flat notes along with F and B notes, in western music.
If a Sharp / Flat key is chosen as tonic note and ONLY the black keys are played in a piano/ organ/ keyboard/ harmonium, then these 5 are the ragams played successively. That is if you have only black keys, with tonic note from C#, it is Shuddha Saveri. From D# it is Udayaravichandrika, from F# it is Mohanam, from A-flat it is Madhyamavathi and from B-Flat it is Hindolam.
This statement is true for simplified ragam structure only. Ragams though are more complex in that there are phrases to use and phrases to avoid, gamakas, elongation of notes, a specific mood/ bhava/ rasa to be evoked while singing/ playing, etc. These cannot be captured well in scientific notations.
The difference between this set and Mohanam set shown above it, is that the 3rd note differs between E and D# (reference note purpose only). Hence, Shivaranjani differs from Mohanam by one note – G2 in place of G3, Revati differs from Madhyamavati by one note – R1 in place of R2, while Sunadavinodini differs from Hindolam in all notes other than S (as that step is equivalent of shifting down tonic note, Sa, by one note while retaining all other notes of Hindolam).