History of Indian music, lost in antiquity, is so interwoven with mythology and legends, that it is surrounded by misconceptions and mystery. In spite of this, Indian music has maintained it’s characteristics in it’s highly developed melodic and rhythmic structure. Traditionally, the history of Indian music is divided into three periods. They are:
 The Ancient period (6000 BC? to between 200 BC and 400 AD)
 The Medieval period (400 AD to 1500 AD)
 The Modern period (1500 AD onwards)
2.1 Naada, shruti, swara [Musical sound or tone, microtone, note]
Naada is a musical sound. It is a series of regular vibrations in a medium like air (as opposed to irregular vibrations, which would be heard as noise). The frequency of a vibration decides the pitch of the sound it represents (how high or low the sound feels to the ear). The frequency is reported in a unit called Hertz (Hz). The frequency range of a sound the human ear can hear is 20 Hz to 20,000 Hz.
Now, as an example, take a sound (or tone) having a frequency of 100 Hz. Another sound, having twice the frequency, that is, 200 Hz, will sound the same. But it will sound ‘higher’. The frequency ratio 200:100, which is 2:1, represents what is called an octave. The number of sounds that the human ear can hear, in an octave, is infinite. But the number of sounds that it can discern, differentiate, or grasp, is 22. They are called shruti-s (microtones). Shruti has been variously translated as: microtone, microtonic interval, interval, step etc. It is mainly determined through fine auditory perception
So, to continue with our example, there exist 22 shruti-s, starting with the first shruti on the starting point of 100 Hertz. Taking the sound represented by 100 Hz as the point of reference, we get 22 ratios. The 23rd ratio takes us to the sound represented by 200 Hz. These ratios are called intervals. The intervals are measured in relation to the reference sound (100 Hz in our example). The octave is represented by the ratio 200:100, or the interval 2:1. This sound of reference is called tonic, key, or “Sa”, etc. In Indian musical terminology, it is known as shadja, “Sa” for short. It is represented by the symbol S. Out of the 22 shruti-s, 7 are selected to form a musical scale. The tonic is fixed first, followed by 6 more shruti-s to form a 7-ladder scale. These 7 sounds, or tones, are called swara-s (or notes). The tonic, in our example, would fall on the sound represented by 100 Hz. This would be our “Sa (S)”. The Sa would be followed by 6 more notes, 7 in all. The 8th note, the sound represented by 200 Hz, would sound like the tonic, but it would sound “higher”. The 7 notes form the “saptaka” of Indian music; the 8 notes– the eighth note being the “higher” Sa — form the “octave” of the Western music. The seven notes are named as follows:
shadja, “Sa” for short, symbol S; rishabha, “Re”, R; gandhara, “Ga”, G; madhyama, “Ma”, m; panchama, “Pa”, P; dhaivata, “Dha”, D; and the 7th, nishada, “Ni”, N.
For convenience, let us call the Western musical note, C, as our tonic, the “Sa”. Then the seven notes would be: C, the “Sa”; D, “Re”; E, “Ga”; F, “Ma”; G, “Pa”; A, “Dha”; and the 7th, B, “Ni”.The first and the fifth notes, namely C (Sa) and G (Pa), are regarded immutable (“achala”). The remaining 5 notes have two states each. Thus we have 12 notes in an octave. The 12 notes are designated short names and symbols as under:
# Name Symbol
1 Sa shuddha (natural) S C 1st white
2 Re komala (flat) r D flat 1st black
3 Re shuddha (natural) R D 2nd white
4 Ga komala (flat) g E flat 2nd black
5 Ga shuddha (natural) G E 3rd white
6 Ma shuddha (natural) m F 4th white
7 Ma teevra (sharp) M F sharp 3rd black
8 Pa shuddha (natural) P G 5th white
9 Dha komala (flat) d A flat 4th black
10 Dha shuddha (natural) D A 6th white
11 Ni komala (flat) n B flat 5th black
12 Ni shuddha (natural) N B 7th white
The octave can be divided into two equal parts: the lower tetrachord, consisting of C-D-E-F, and the upper tetrachord, made up of G-A-B-C. This last-mentioned C has the interval 2:1 with the first C in the lower tetrachord. The lower tetrachord is called “poorvaanga” (poorva + anga), the upper tetrachord, “uttaraanga” (uttara + anga) in Indian musicology. Further, Full expression of Indian music requires up to 3 octaves. They are: the “mandra saptaka” (lower octave), the “madhya saptaka” (middle octave), and the “taara saptaka” (higher octave). Note: The notes in Western music use the tempered scale, while in Indian music the notes use the natural harmonic scale.