Shruti (music)

The śruti (Sanskrit "thing heard", "sound") is the smallest interval of the tuning system of Indian classical music. Canonically, there are 22 śruti in the octave, although systems with more or fewer śruti have been proposed. Here they are given in terms of just intonation, although many authors assume schismatic temperament implicitly.

There are three kinds of śruti:

• The pramāṇa ("measuring" or "standard") śruti, 81/80, equal to the syntonic comma
• The nyūna ("deficient") śruti, 25/24, the difference between a 6/5 minor third and a 5/4 major third
• The pūraṇa ("fulfilling") śruti, 256/243, equal to the Pythagorean limma

Together these three intervals can form any interval of 5-limit just intonation. (In mathematical terms, they form a basis for the vector space.)

Note that the same interval is always composed of the same number of śruti. 16/15 is 2 śruti, 10/9 is 3 śruti, 9/8 us 4 śruti, 4/3 is 9 śruti, 3/2 is 13 śruti, and the 2/1 octave is 22 śruti.

The word śruti is also used to refer to the pitches themselves. There are two pitches separated by a pramāṇa śruti for every pitch of the Western chromatic scale except the root and the fifth (which are often the two drones), resulting in a total of 22.

Number of śruti above the tonic	Ratio	Cents	Kind of śruti to next pitch	Southern names	Northern names
0	1/1	0	pūraṇa	Shadaja	Shadaja
1	256/243	90.2	pramāṇa	Guali Rishabha, Ekasruti Rishabha	Komal Rishabha
2	16/15	111.7	nyūna	Suddha Rishabha, Dvisruti Rishabha	Madhya Rishabha
3	10/9	182.4	pramāṇa	Trisruti Rishabha	Suddha Rishabha
4	9/8	203.9	pūraṇa	Chatussruti Rishabha	Tivra Rishabha
5	32/27	294.1	pramāṇa	Suddha Gandhara, Bhairavi Gandhara	Ati-komal Gandhara
6	6/5	315.6	nyūna	Shatsruti Rishabha, Sadharana Gandhara	Komal Gandhara
7	5/4	386.3	pramāṇa	Antara Gandhara	Suddha Gandhara
8	81/64	407.8	pūraṇa	Chyuta Madhyan Ga, Tivra Antara Ga	Tivra Gandhara
9	4/3	498.1	pramāṇa	Suddha Madhyama	Suddha Madhyama
10	27/20	519.6	nyūna	Begada Madhyama, Tivra Suddha Ma	Ekasruti Madhyama
11	45/32	590.2	pramāṇa	Prati Madhyana	Tivra Madhyama
12	64/45	409.8	pūraṇa	Chyutta Panchama	Tivratara Madhyama
13	3/2	701.9	pūraṇa	Panchama	Panchama
14	128/81	792.2	pramāṇa	Ekasruti Dhaivata	Ati-komal Dhaivata
15	8/5	813.7	nyūna	Suddha Dhaivata, Dvisruti Dhaivata	Komal Dhaivata
16	5/3	664.3	pramāṇa	Trisruti Dhaivata	Suddha Dhaivata
17	27/16	905.9	pūraṇa	Chatussruti Dhaivata	Tivra Dhaivata
18	16/9	996.1	pramāṇa	Suddha Nishada, Komal Kaisiki Ni	Ati-komal Nishad
19	9/5	1017.6	nyūna	Shatsruti Dhaivata, Kaisiki Nishada	Komal Nishad
20	15/8	1088.3	pramāṇa	Kakali Nishada	Suddha Nishad
21	243/128	1109.8	pūraṇa	Chyuta Shadia Nishada	Tivra Nishad
22	2/1	1200	pūraṇa	Shadaja	Shadaja

See also

• Sruti box

References

• Lentz, Donald A. Tones and Intervals of Hindu Classical Music. University of Lincoln, 1961.