Istrian scale is a two-part singing of both unique genres of musical folk music from Istria and Kvarner that is employed in the style.
Istrian folk music consists of a distinctive six-tone musical scale (the so-called Istrian scale) and two-part, slightly nasal singing typical of the peninsula. Instrument types include double reeds such as sopele, shawms, and bagpipes, as well as flutes and tambura lutes; genres include kanat and tarankanje, variations, and improvisations, and resolution to unison or octave; and techniques include nasal tone and improvisations. The term was first used by Ivan Mateti Ronjgov, who was studying and notating Croatian music in the twentieth century.
Croats, Istro-Romanians, and Italians all preserve a variety of two-part singing and playing in the Istrian scale on the Istrian peninsula in western Croatia. This style is characterized by vigorous, partly nasal singing, involving a degree of variation and improvisation in both vocal parts, but always culminating in two performers singing in unison or octaves apart. Local sub-styles have developed distinct features of their own. A typical example of this is kanat, where the second voice is often switched for or doubled, imitating the sound of a small sopele. The widespread variant, tarankanje, replace words with syllables (ta-na-na, ta-ra-ran, etc.) that imitate the sound of a flute.
The distinctive vocal singing of Istria and the Kvarner Gulf takes the form of half-steps and whole-steps alternated with untempered performances, particularly by older singers and instrumentalists. A characteristic two-part polyphony of minor thirds (or major sixths) and a cadence to unison or an octave is sung by pairs of singers (male, female, or mixed). Singers distinguish higher (na tanko 'thin') from lower (na debeno 'fat') parts of the song.
The non-equal-tempered scale would look like this: E-F-G-A - B - C [hexatonic] (see enharmonic), the first six notes of an octatonic scale on E. However, "relative intonation varies considerably from example to example [and instrument to instrument]," the scale has also been described as a structure of subharmonics seven to fourteen (approximately D, E, F, G, A, B, C, D') with two voices.
As of today, the Istrian two-part singing is still practiced in everyday life and on special occasions, such as weddings, community gatherings, and religious services. There are a hundred outstanding singers and musicians and ten craftspeople, that bear the tradition, and learned their skills and knowledge from their elders. Today, they often attend organized folklore groups around the area.
References
(https://ich.unesco.org/en/RL/two-part-singing-and-playing-in-the-istrian-scale-00231) (https://en.wikipedia.org/wiki/Istrian_scale)