The ambiguity of free jazz presents problems of definition. Although it is usually played by small groups or individuals, free jazz big bands have existed. Although musicians and critics claim it is innovative and forward-looking, it draws on early styles of jazz and has been described as an attempt to return to primitive, often religious, roots. Although jazz is an American invention, free jazz musicians drew heavily from world music and ethnic music traditions from around the world. Sometimes they played African or Asian instruments, unusual instruments, or invented their own. They emphasized emotional intensity and sound for its own sake, exploring timbres.