The Saptak literally evolves from the Shadja, or the sa, which is the base note or the aadhaar swar. Shadja itself means that which gives birth to six (more). What this also means is that the saptak can not exist without the shadja. It is only when you define the shadja, the sa, that the positions of the others will automatically be defined.
The positions of the rest of the swara arise from the principle of consonance, and bear specific relation (in pitch) with the sa. Thus, each swara also holds a specific relationship with every other swara. parental security . It is every musician’s quest to explore these relationships, and use them for music making.
The clip below should generally explain how the saptak is formed.
It is important here to dwell upon the concept of consonance (Samvaad). Consonant relationships between two notes are a natural preference of the human ear (physiologically), and result in the experience of pleasure. The degree of the pleasure varies, and depends upon the exact relationship.
The opposite of consonance is dissonance (Visamvaad) and it results in displeasure. Any two notes separated by a half note distance have this dissonant relationship. So the Sa and the komal Re (or the Ni) would be dissonant or visamvaadi with each other.
However, it does not mean that the dissonance is avoided altogether while making music. (It would perhaps be like writing a story or making a movie with only happy scenes). Rather, the dissonance is also used aesthetically, and in fact some of our Ragas like Shree and Marwa exploit it to the fullest. Generally though, Indian music avoids using two consecutive half notes one after the other. The whole concept will be clearer when we move on to the shadja pancham bhaav and the aesthetics within the saptak. But that would be for later.
Understanding all the swara positions perfectly, and being able to produce these with respect to the shadja is the part of training to become a musician. What exactly is “perfection” of the swara? And what is a Surila musician? I think this deserves to be a separate topic for a post, which will be my next.
There are also various other things related to the saptak, such as comparisons with other (mainly western and the carnatic) scales, tempering of the scale, the tanpura etc…We will touch upon these subsequenly…..
I commented earlier upon the danger of over- simplification ( at least initially) when we are trying to explain such abstracts. I would once again ask you to view the explanatory AVs with this in mind, as they would sometimes prove to be a bit inadequate, but I hope the discussion here would fill any gaps.