Wikipedia
The Obikhod is a collection of polyphonic Russian Orthodox liturgical chants forming a major tradition of Russian liturgical music which includes both liturgical texts and psalm settings.
The original Obikhod, the book of habits of the monastery of Volokolamsk was composed about 1575, among the subjects of the book were chants.The Obikhod was originally monodic but later developed polyphony. The Obikhod became the first music printed in Russia, in Moscow, in 1772. The common version was heavily revised and standardized by Rimsky Korsakov leading to the 1909 edition of the Obikhod, the last before the Revolution.
The Obikhod style, and the 1909 edition, became dominant during the 20th Century displacing both Russian styles such as the Ruthenian Prostopinije style and also the chant traditions of Georgia, Armenia, and Carpatho-Russia.
The Obikhod chants are utilised in Nikolai Rimsky-Korsakov's Russian Easter Festival Overture, in Anatoly Lyadov's Ten Arrangements from Obikhod Op.61, and in Alexander Raskatov's Obikhod (2002).
The pitch set used in these chants traditionally consists of four three-note groups. Each note within a group is separated by a whole tone, and each group is separated by a semitone. If starting from G, the result is: G, A, B / C, D, E / F, G, A / B♭, C, D. Theoretically, more groups can be added either above or below, which has been done by some 20th century Russian composers. This pitch set has influenced Russian folk music as well: for example, the Livenka accordion contains the pitch set on its melody side.