Improvisation is a method of musical performance, whereby there is an absence of any prior conventional composition. Improvisation can be performed either solo ,or as a ensemble.
In cases where more than one person is performing, interesting cogno-social and musical mechanisms must be used, as if as a means of communication.
In some cases, performers may rely upon graphic scores, but these scores are ambiguous and allow for free interpretation usually within given limits.
LOcated below are some examples of graphic scores. Improvisational pieces seldom have a set duration or length, although it is quite common for such pieces to progress the 1 or more movements, especially with regard to pieces that are based on graphic scores.
As is also apparent, graphic scores themselves can sometimes be regarded as independent works of art.
Interesting improvisation based blog:- http://ericbarnhill.wordpress.com/facts-about-improvisation
Located below is a list of improvisation based ensembles:-
The A Band
Birdyak (a duo consisting of Bob Cobbing and Hugh Metcalfe)
The Brotherhood of Breath
Iskra 1903 (a trio led by Paul Rutherford, with Barry Guy and either Derek Bailey or Philipp Wachsmann)
Last Exit (1980s group)
Music Improvisation Company with Derek Bailey, Evan Parker and Hugh Davies
Musica Elettronica Viva
nmperign (a duo consisting of soprano saxophonist Bhob Rainey and trumpeter Greg Kelley)Ovary Lodge, centered around Keith Tippett, Julie Tippetts and Frank Perry
poire z – electronics
Shaking Ray Levis
The Sperm – Finnish improv group of early 70s featuring Pekka Airaksinen
Spontaneous Music Ensemble
Triangulation – Irish-Swiss-French improv group with Christy Doran, John Wolf Brennan, Patrice Héral and Bruno Amstad
Un Drame Musical Instantané and precursor Birgé Gorgé Shiroc
Wired, featuring Conny Plank
Vitamin S – A free improvisation collective