A GENRE OF MUSIC LIKE JAZZ that relies so fundamentally on improvisation is by necessity different from one performance to the next. The transient nature of music in general is further emphasized by this practice in jazz. Jazz has been described as “defying notation” (Schuller, x), as much of the music is played without the aid of a score and its wide range of timbres, for example, is difficult to capture in conventional musical notation. Together with the central role of improvisation, this lack of notation helps to create “an aesthetic of sheer presentness” (Rice, “‘It Don't Mean a Thing,’” 170) in jazz music to an extent that is not found in most other genres. Of course a performance of classical music is also evanescent, but there is not the same emphasis on presence as in jazz, since a performance is perceived as being to a much greater extent repeatable. Classical musicians generally aim to reproduce an idealized version of the music, rather than to make it completely new; a dress rehearsal allows the coordination of tempi, dynamics, and other features that can thus be reproduced in essentially the same way in the performance. The difference between performances of classical music and jazz lies primarily in a culture that emphasizes the transience, changeability, and newness of jazz, as opposed to fidelity to a score in classical music. A comparison of jazz recording practice with that of classical music is also revealing in this context. Jazz musicians often record and release several different takes of the same piece—such as Charlie Parker's multiple versions of “Ornithology”—as each performance is seen to be essentially different.