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Theshruti orśruti[ɕrʊtɪ] is the smallestinterval ofpitch that thehuman ear can detect and a singer or musical instrument can produce.[1][2] The concept is found in ancient and medieval Sanskrit texts such as theNatya Shastra, theDattilam, theBrihaddeshi, and theSangita Ratnakara.[1][3]Chandogya Upanishad speaks of the division of the octave in 22 parts.[4]
Theswara differs from theshruti: theshruti is the smallest gradation of pitch available, while aswara is the selectedpitches from which the musician constructs thescales,melodies andragas. TheNatya Shastra identifies and discusses twenty twoshruti and sevenswara peroctave.[1][3][5]
It has been used in several contexts throughout the history ofIndian music. Recent research has more precisely defined the termshruti, its difference fromnada andswara, and identified positions on a string to play 22 shrutis.[6][7][8]
The most well-known example of shrutis is probably the use of the ati-komal (extra flat) gandhar inragaDarbari. Others include the rishabh in Bhairav, the nishad in Bhimpalasi and Miya Malhar, and the gandhar in Todi.
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The meaning ofshruti varies in different systems.[9]
Bharata Muni uses shruti to mean the interval between two notes such that the difference between them is perceptible.[10]
In the current practice ofCarnatic music,shruti has several meanings.[11]
In certainragas, due to inflexions orgamakas on some of those 12 notes, listeners perceive a sharpened or flattened version of an existing note.[12]
Some scientific evidence shows that these intermediate tones perceived in the contemporary rendition of a raga do not hint at the existence of 22 shrutis. The number 22 is not practically significant in the current performance of Carnatic and Hindustani music traditions, partly because different musicians use slightly different "shrutis" when performing the same raga, an example being the ati-komal (extra flat) gandhar inDarbari. The phenomenon of intermediate tones is pursued as an active area of research in Indian Musicology, which says the number of perceptible intermediate tones may be less or more than 22.[12]
An Indian monograph about shruti claims various opinions about the number of shrutis. In recent times the number is broadly agreed upon to be 22. Recognizing the controversy over the number and the exact ratios of shruti intervals, it also says that not allshruti intervals are equal[13] and known aspramana shruti (22%),nyuna shruti (70%) andpurana shruti (90%).[14] Eachshruti may be approximated in the53EDO system.[15]
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Shruti is linked to the fundamental aspects ofswara.[16] Of the twenty twoshruti,veena scholars identified the 4thshruti as thesasolfege, 7th asre, 9th asga, 13th asma, 17th aspa, 20th asdha, and 22nd asni.[17]
In performance, notes identified as one of the 12 universal pitch classes of the chromatic scale (swara-prakara) are theshrutis, and connected unidentified notes between them arenadas. The human ear takes about 20–45 msec to identify a note within the range of the human voice—from 100 to 1000 Hz.[18] The ear can identifyshrutis played or sung longer than that—but cannot identifynadas played or sung faster than that limit, but can only hear them. Lack of appreciation of this difference has led to many scientists to opine that because of the meend and the oscillating notes, it is hard to determine the exact numerical frequencies.[19]
In ancient times,shruti was described in Sanskrit asShruyate iti Shruti, meaning "What is heard is a shruti". The "understanding" and "learning" part is the natural fact that on 22 specific points on a string, the perception of notes changes.[20]
Brihaddeshi (Sanskrit) by Pandit Matanga mentions after Shloka 24, in Shrutiprakarana (Chapter on Shrutis) that "[o]nly when the ear understands (the point on the string where perception of the notes changes), does that sound become a Shruti." He further says that these points on the string are very precise, as in Shloka 28, Chapter 1, in Nadaprakarana (Chapter on Nadas) that "[r]eaching (the point on the string where the perception of the notes changes), and reverting (from there) results in the precision that is called as 'Shruti.'"[21]
There are 12 universally identifiable musical notes (pitch classes of the chromatic scale or Swara-prakara) in an octave. They indicate "a musical note or scale degree, but Shruti is a more subtle division of the octave".[16]
When the frequency and positions of all 22shrutis are calculated, three ratios exist: 256/243 (Pythagorean limma,Pythagorean diatonic semitone, orPythagorean minor semitone), 25/24 (a type ofjust chromatic semitone), and 81/80 (syntonic comma). Out of these, 81/80 operates in the 'region' of 10 notes and is calledpramana (transl. "standard", region of the note). The 256/243 ratio is calledpoorna (transl. "big"), and 25/24nyuna (transl. "small").Poornas come betweenshrutis 0–1, 4–5, 8–9, 12–13, 13–14, 17–18, and 21–22,nyunas betweenshrutis 2–3, 6–7, 10–11, 15–16, 19–20, andpramanas betweenshrutis 1–2, 3–4, 5–6, 7–8, 9–10, 11–12, 14–15, 16–17, 18–19, 20–21.[22][unreliable source?]
In any gamaka, onlyshrutis andnadas exist. The threshold of identification of a musical note within the range of human voice of 100–1000 Hz is 20–45 msec.[18]Shrutis can be identified by the human ear because they are played for this time limit at the fastest. In contrast, connectingnadas are played faster than this limit, which prevents the human ear from identifying them. The major difference in the two systems is the way they combine shrutis and connect nadas, resulting in characteristically different music between the styles. Many ancient Sanskrit and Tamil works refer to the 22shrutis as the foundation of the Indian Music Scale.[22]
The system of 72 basic types of singing or playing scales (thaļas) evolved with specific mathematical combinations of the universal 12 pitch classes. The selection of the 22shrutis in each of them depends on therāga chosen. Theshrutis in arāga should be ideally related to each other, by natural ratios 100:125, 100:133.33, 100:150, and 100:166.66. Arāga can have a fewer number of notes than in athaļa.[22]
Some suggest that the best way to find the exact positions of shrutis is by analyzing the frequencies players use in actual performances.[19] When different artists performedrāgayaman on flute, sarangi, sitar, and voice, pitch accuracy was found to be "relative" and "subjective",[23] and "neither rigidly fixed" "nor randomly varying";[24] the "same Swara was pitched differently at different times by the same artiste in the same raga", and "different artistes intoned the same swara differently in the same raga".[25]
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