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Yass (jass) is a Polish music style of avant-garde jazz which originated in the late 1980s, that mixes jazz, improvised music, punk rock, and folk. The style began with Avant-Garde Jazz musicians from the Tricity and Bydgoszcz, where the Jazz club Mózg became the unofficial 'home venue' for Yass performers, with its own label releasing a number of Yass productions.
The term Yass was coined by bassist and guitarist Tymon Tymański, clarinetist Mazzoll and guitarist Tomasz Gwinciński, who wanted to stress the novelty of the new style. The first Yass album is generally regarded to be Tańce bydgoskie by Trytony. 
Though it frequently crosses genres, Yass music can be broadly described as a frequently arrhythmic and highly improvised style of Jazz. The most seminal period for Yass was in the 1990s, with many active groups performing and releasing albums, including Miłość, Łoskot, Trytony, and Mazzoll & Arhythmic Perfection. A good overview of the Yass scene exists on the compilation album Cały ten Yass! released by Jazz Forum magazine shortly after the genre's heyday.
Free improvisation or free music is improvised music without any rules beyond the logic or inclination of the musician(s) involved. The term can refer to both a technique and as a recognizable genre in its own right.
Free jazz is a style of avant-garde jazz or an experimental approach to jazz improvisation that developed in the late 1950s and early 1960s when musicians attempted to change or break down jazz conventions, such as regular tempos, tones, and chord changes. Musicians during this period believed that the bebop and modal jazz that had been played before them was too limiting, and became preoccupied with creating something new. The term "free jazz" was drawn from the 1960 Ornette Coleman recording Free Jazz: A Collective Improvisation. Europeans tend to favor the term "free improvisation". Others have used "modern jazz", "creative music", and "art music".
Krautrock is a broad genre of experimental rock that developed in West Germany in the late 1960s and early 1970s. It originated among artists who blended elements of psychedelic rock, avant-garde composition, and electronic music, among other eclectic sources. Common elements included hypnotic rhythms, extended improvisation, musique concrète techniques, and early synthesizers, while the music generally moved away from the rhythm & blues roots and song structure found in traditional Anglo-American rock music. Prominent groups associated with the krautrock label included Neu!, Can, Faust, Tangerine Dream, Kraftwerk, Cluster, Ash Ra Tempel, Popol Vuh, Amon Düül II and Harmonia.
Jan Garbarek is a Norwegian jazz saxophonist, who is also active in classical music and world music.
Naked City was an avant-garde music group led by saxophonist and composer John Zorn. Active primarily in New York City from 1988 to 1993, Naked City was initiated by Zorn as a "composition workshop" to test the limits of composition in a traditional rock band lineup. Their music incorporated elements of jazz, surf, progressive rock, classical, heavy metal, grindcore, country, punk rock, and other genres.
Erstwhile Records is an independent record label devoted to free improvisation, particularly the electroacoustic variety, contemporary, experimental composed music, and combinations of both. Erstwhile was founded by Jon Abbey in 1999, whose personality and tastes are closely identified with the label.
Igor Grigoriev, is a musician, composer, arranger, band leader, and improvisational guitarist. He taught himself to play the guitar as a young child, and later obtained his master's degree from a music institution in Russia.
Straight-ahead jazz is a genre of jazz that developed in the 1960s, with roots in the prior two decades. It omits the rock music and free jazz influences that began to appear in jazz during this period, instead preferring acoustic instruments, conventional piano comping, walking bass patterns, and swing- and bop-based drum rhythms.
European free jazz is a part of the global free jazz scene with its own development and characteristics. It is hard to establish who are the founders of European free jazz because of the different developments in different European countries. One can, however, be certain that European free jazz took its development from American free jazz, where musicians such as Ornette Coleman revolutionised the way of playing.
Post-bop is a jazz term with several possible definitions and usages. Musicologist Barry Kernfeld wrote in The New Grove Dictionary of Music and Musicians that post-bop is "a vague term, used either stylistically or chronologically to describe any continuation or amalgamation of bop, modal jazz, and free jazz; its meaning sometimes extends into swing and earlier styles or into fusion and third-world styles." The term has been variously defined as a musical period, a musical genre, a musical style, and a body of music, sometimes in different chronological periods, depending on the writer.
Polish jazz has a history that spans periods of both acceptance and political repression.
The Avant-Garde is an album credited to jazz musicians John Coltrane and Don Cherry that was released in 1966 by Atlantic Records. It features Coltrane playing several compositions by Ornette Coleman accompanied by the members of Coleman's quartet: Cherry, Charlie Haden, and Ed Blackwell. The album was assembled from two unissued recording sessions at Atlantic Studios in New York City in 1960.
Miłość was a Polish Yass music band. The band was founded in 1988 by Ryszard Tymon Tymański, double bassist and guitarist, former leader of new wave group Sni Sredstvom Za Uklanianie. Miłość played free jazz with avantgarde influences and gave birth to, among others, the Tricity and Bydgoszcz jazz bands, and to a style called yass. Miłość recorded two albums with the legendary jazzman Lester Bowie: "Not Two" (1995) and "Talkin' About Life and Death" (1999). The band split up after Olter's death in 2002.
Punk jazz is a genre of music that combines elements of jazz, especially improvisation, with the instrumentation and performance style of punk rock. The term was first used to describe James Chance and the Contortions' 1979 album Buy. Punk jazz is closely related to free jazz, no wave, and loft jazz, and has since significantly inspired post-hardcore and alternative hip hop.
The Muffins were an American Maryland-based progressive rock/avant-jazz group. They were formed in Washington, DC in the early 1970s and recorded four albums before disbanding in 1981. In 1998 the group reformed and recorded a further five albums and a DVD. The Muffins played at Symphony Space on Broadway in NYC with Marion Brown in 1979, and also performed at a number of festivals, starting with the ZU Manifestival in New York City in 1978, The Villa Celimontana festival in Rome, Italy in 2000, two appearances at Progday in 2001 and 2002, NEARfest in 2005, and the "Rock in Opposition" festival in France in 2009. In 2010, The Muffins headlined at Progday, making a third appearance at this long running festival.
Experimental rock, also called avant-rock, is a subgenre of rock music that pushes the boundaries of common composition and performance technique or which experiments with the basic elements of the genre. Artists aim to liberate and innovate, with some of the genre's distinguishing characteristics being improvisational performances, avant-garde influences, odd instrumentation, opaque lyrics, unorthodox structures and rhythms, and an underlying rejection of commercial aspirations.
Andrzej Grzegorz Przybielski was a Polish jazz trumpeter associated with the avant-garde jazz and free jazz scenes.
Mat Walerian is a jazz saxophonist and woodwind player, composer and bandleader who specializes in improvisation and avant-garde music.
Guitar, Drums 'n' Bass is an album by free improvisation guitarist Derek Bailey, released by Avant Records in 1996. After spending several years improvising his guitar to the sound of jungle and drum and bass music on pirate radio, Bailey proposed to collaborator John Zorn that he make an album of his musical fusion. Zorn then contacted Birmingham-based drum and bass producer D.J. Ninj to provide the musical backing, who recorded his contributions in spring 1995. After a failed session with engineer Mick Harris, Bailey recorded his overlaid guitar improvisations in Bill Laswell's New York City studio in October 1995, slightly altering Ninj's contributions to remove electric piano passages.
Spiritual jazz is a sub-genre of jazz that originated in the United States during the 1960s. The genre is hard to characterize musically but draws from free, avant-garde and modal jazz and thematically focuses on transcendence and spirituality. John Coltrane's 1965 album A Love Supreme is considered landmark in the genre.