Experimental film or experimental cinema describes a range of filmmaking styles that are generally quite different from, and often opposed to, the practices of mainstream commercial and documentary filmmaking. "Avant-garde" is also used to describe this work, and "underground" has been used in the past, though it has also had other connotations. While "experimental" covers a wide range of practice, an "experimental film" is often characterized by the absence of linear narrative, the use of various abstracting techniques (out of focus, painting or scratching on film, rapid editing), the use of asynchronous (non-diegetic) sound or even the absence of any sound track. The goal is often to place the viewer in a more active and more thoughtful relationship to the film. At least through the 1960s, and to some extent after, many experimental films took an oppositional stance toward mainstream culture. Most such films are made on very low budgets, self-financed or financed through small grants, with a minimal crew or, quite often, a crew of only one person, the filmmaker. It has been argued that much experimental film is no longer in fact "experimental," but has in fact become a film genre and that many of its more typical features - such as a non-narrative, impressionistic or poetic approaches to the film's construction - define what is generally understood to be "experimental".