Sāmagāna is not merely a name given to singing hymns of Veda but represents the philosophy and science of uniting thought, sound and music.
Sāma is singing of hymns from Rigveda alone and not from other Veda-s. "richi adhyoodham sama" ऋचि अध्यूढ्रम साम (Chhandog Upnishad 1.6.1).
The richā-s or hymns of Rigveda are called yoni or ādhāra as they form the base of Sāmagān.
Jaimineeya जैमिनीय Ārchika grantha (treatises) contains hymns that are yoni or base to Gāna or singing.
Sāma created on richa-s of Poorvārchika are called Grāma-gāna,ग्रामगान् Grāmegeya-gāna, ग्रामगेयोगान् Prakriti-gāna प्रकृतिगान or Veya-gāna वेयगान्.
Sām created on richa-s of Uttarārchik are known as Ooha-gāna.ऊहगान् The Sanskrit root ooh means 'to modify according to need'.
They are so conceived, because the telling notes of the voice in its upper register, and this presents itself, therefore as the starting point for a vocal scale."
The Sāyana#-bhāshya (critique) on Sāma-vidhāna Brāhmana establishes that note of Sāma were of nidhana prakriti (diminishing nature) and followed a descending order.
A higher note determined was called Krushta after Sanskrit root Krush (to scream, speak loudly).
So the complete Sāmic Saptaka in descending order contains: To preserve the Sāmik notes, Raga Sāmeshwari was created.
Dr. Lalmani Misra first translated the notes M G R S D N P into Shadja gram—S N D P G M R—and then created a Raga which is performed in the evening.
There are five with individual signs for three shruti-jāti-s. A Rishi in Rig Veda is an author of a Rik, a hymn mantra, derived from oral tradition and direct insight, not from reasoning or intellect.
[citation needed] Sri Aurobindo described Shruthi as "divine recordings of cosmic sounds of truth" heard by the Rishis.