Ṛiṣabha/Risabha/Rishabh is the 2ndsvara from the 7 svaras of Hindustani music. Risabha is the long form of the syllables रे and री. For simplicity in pronouncing while singing the syllable, Risabha is pronounced as Re and Ri. It is also called as ऋषभ.
It is said that Sadja is the basic svara from which all the other 6 svaras are produced. When we break the word Sadja then we get, Shad And Ja. It means that Shad is 6 and ja is 'giving birth' in marathi. So basically the translation is :
षड् - 6, ज -जन्म. Therefore, it collectively means giving birth to the other 6 notes of the music. So the svara Re is formed from Sadja.
The frequency of Risabha is 270 Hz. The frequencies of the 7 svaras are also given below: Sa 240 Hz, Re 270 Hz, Ga 300 Hz, Ma 320 Hz, Pa 360 Hz, Dha400 Hz, and Ni 450 Hz, Sa 480 Hz .........
Consequently, the Re after the Sa of 480 Hz has a frequency of 540 Hz i.e. the double of the Lower octave Re.
There are 3 Shruti's of Risabha. Previously the main Shruti, not only for Re but for all the other svaras, was on the last Shruti but now it is considered to be on the 1st Shrurti.
For example, if these are the 3 Shruti's of Re then, Previously this was the position of the main Shruti of Re. ^ 1 2 3 ^ But now this position has become the main Shruti of Re.
All the other svaras except Sadja and Pancham can be Komal or Tivra svaras but Sa and Pa are always Shuddha svaras. And hence svaras Sa and Pa are called Achal Svaras, since these svaras don't move from their original position. Svaras Ra, Ga, Ma, Dha, Ni are called Chal Svaras, since these svaras move from their original position.
Sa, Re, Ga, Ma, Pa, Dha, Ni - Shuddha Svaras
Re, Ga, Dha, Ni - Komal Svaras
Ma - Tivra Svaras
Ragas from Bhairav That, Poorvi That, Marwa That, Bhairavi That and Todi That, have Komal Risabha.
Ragas where Re is the Vadi svara - Raga Brindabani Sarang, etc. Ragas where Re is the Samvadi svara - Raga Bhairav, etc.
Hypothetically speaking, Re is said to be the Rishimuni, Rishimuni as in, the three main gods, Bhrama, Vishnu and Shiva were first created i.e. Sarkar and then these three gods created Rishimuni i.e. Re. Re is made the acronym of Rishimuni for showing the importance of the syllable Re.
Risabha is said to be sourced from the lowing of a bull.
Difference in pronouncing
In the introductory part of Risabha it is given that, 'Risabha is the long form of the syllables रे and री. For simplicity in pronouncing while singing the syllable, Risabha is pronounced as Re and Ri'. This given because the pronouncing of the syllable Re is different in the Hindustani classical music and Carnatic classical music. In Hindustani classical music, the pronouncing of Risabha is done as Re and in Carnatic classical music, the pronouncing of Risabha is done as Ri. So a Hindustani classical singer will sing the 7 svaras as : Sa Re Ga Ma Pa Dha Ni Sa. While a Carnatic classical singer will sing these svaras like : Sa Ri Ga Ma Pa Dha Ni Sa.
