Improvisation
The author investigates, on the basis of representative music samples, the techniques of spontaneous creation in various periods of jazz history, techniques which are commonly referred to in popular jazz parlance as "improvisation". In the older forms, the music of country brassbands, street bands, spirituals, work songs and ballads of the archaic period of Afro-American music, the author discovers an improvisational practice based on the paraphrase of a given melody without change of rhythmic structure. This practice, which Marius Schneider in his History of Polyphony has termed "variational heterophony", creates melodic variation through linear or simultaneous tone substitution: the original tones of the melody being replaced by intervals most closely related to them harmonically. This tone substitution is determined by a set tone-skipping procedure, e.g. the tone before the proceding tone or the one after the following tone of any given tone within a scale is used in place of it.
Apart from the practice of tone substitution there exists a second technique consisting of spontaneous change of the melody through rhythmic variation: such rhythmic devices consist of anticipating and retarding off-beat accentuation and phrasing, rhythmic diminuation, augmentation, and inversion. Typical of this rhythmic paraphrasing is retaining unchanged the original melodic structure.
During the period of classical jazz these improvisational methods were skillfully developed to a complete melodic restructuring. Preferred devices are inversions of the speed and direction of the tone progression. Actual artistic devices consisted of spontaneously restructuring the basic melody into definitely new forms, e.g. AABA into a shout-chorus or blues. The technique of rhythmical change is further elaborated through formative patterns employed isorhythmically: stomping and stomp choruses. All of these improvisational techniques are employed in strict adherence to characteristic Afro-American tonality, harmony, articulation and intonation. The elaboration of these popular forms of instrumental playing into the ambitious shapes of subsequent jazz styles was carried out by replacing simple creative forms by artistic elements stemming from European music. This process, in its earlier phases, is illustrated by an example of the improvisation of Louis Armstrong, which brings out his importance in the evolution of jazz style as well as his role as a mediator of exceptional stature.