Hindustani Classical Music: Thaat system

• 7-note octave: In the Indian subcontinent, the 7 most commonly known musical notes (swaras) are called 1) Shadja(S), 2) Rishabha(R), 3) Gandhara(G), 4) Madhyama(M), 5) Panchama(P), 6) Dhaivata(D), and 7) Nishada(N). Together they constitute the most commonly known musical scale, the 7-note octave (saptaka). After N, we get back the previous note S but with doubled frequency/pitch, called Taara Shadja(S'). So, S and S' are the same note but different pitches. S' starts the next higher octave. This 7-note octave from S to N is equivalent to the Ionian mode of the Major scale in the Western classical music.
  
• 12-note octave: Getting more involved into the Indian classical music, the whole interval of an octave (saptaka) is taken to include 12 musical notes (swaras)––the previous 7 notes taken as their pure forms/flavors (shuddha) and additionally for some, their alternative forms/flavors (vikrita). In particular, S and P are considered unalterable anchors (achala swara) coming only in pure (shuddha) flavors whereas rest of the notes are considered to be coming in two flavors each––R, G, D and N in pure (shuddha) and flat (komala) flavors, and M in pure (shuddha) and sharp (teevra/kari) flavors. Thus, the 12-note octave consists of––1) Shadja(S), 2) Komala Rishabha (r), 3) Shuddha Rishava(R), 4) Komala Gandhara(g), 5) Shuddha Gandhara(G), 6) Shuddha Madhyama(M), 7) Teevra/Kari Madhyama(m), 8) Panchama(P), 9) Komala Dhaivata(d), 10) Shuddha Dhaivata(D), 11) Komala Nishada(n) and 12) Shuddha Nishada(N). In the Western Classical music, this 12-note octave is called the Chromatic scale and the difference between two adjacent notes in the Chromatic scale is called semitone. Semitone is the smallest interval generally considered in the Western classical music.
• 22-note octave: Getting even more involved, the whole interval of an octave (saptaka) is taken to include 22 musical notes (shrutis), consisting of the previous 12 notes and further, an additional flavor for each of 10 of these 12 notes, leaving S and P fixed as before. Thus, the 22-note octave consists of (using the terminology used by Dr. Vidyadhar Oke)––1) Shadja(S), 2) Atikomala Rishabha(r1), 3) Komala Rishabha(r2), 4) Shuddha Rishabha(R1), 5) Teevra Rishabha(R2), 6) Atikomala Gandhara(g1), 7) Komala Gandhara(g2), 8) Shuddha Gandhara(G1), 9) Teevra Gandhara(G2), 10) Shuddha Madhyama(M1), 11) Ekashruti Madhyama(M2), 12) Teevra Madhyama(m1), 13) Teevratama Madhyama(m2), 14) Panchama(P), 15) Atikomala Dhaivata(d1), 16) Komala Dhaivata(d2), 17) Shuddha Dhaivata(D1), 18) Teevra Dhaivata(D2), 19) Atikomala Nishada(n1), 20) Komala Nishada(n2), 21) Shuddha Nishada(N1), and 22) Teevra Nishada(N2). They also have traditional names. This 22-note octave is considered as the finest musical scale in the Indian tradition because general human perception cannot appreciate intervals smaller than the intervals of notes of this octave. In the Western terminology, intervals smaller than a semitone are called microtones. The Western Classical music has largely been limited to the use of semitones.
• Innumerable tones: Within the interval of an octave, in fact, there lie innumerable tones/frequencies, but they cannot be distinctively considered as musical notes because general human perception cannot grasp such smaller intervals as necessary to appreciate them. They are touched along the way of continuous movement (meend) from one to another of the above 22 notes, but they cannot be perceptibly singled out for singing or playing. All frequencies are generally called nadas. Of all nadas, the above 22 shrutis can be used in music.