Trajectories (A Study in Prosody) is concerned with everything associated with pitch (intervallic relations, harmony, contour, register, and so on). Yet, it evades having to deal with the very pitch itself. 

The main strategy the composer employs is having all of the different voices in constant flux, so they are in continuous transition (glissando) between pitches. This way we never hear a stable pitch that we might use as reference, and so there is no origin, nor a destination, but rather, a trajectory. 

That is all true, with the exception that in the middle of the piece, for the first and only time we hear a long steady note, frozen in time by the entire ensemble. In the scenery of constant motion, the lack of movement becomes (perhaps paradoxically) quite intense. 

To realize his plan, the composer decided to use a string ensemble. The piece is realized in a joined effort by two of the finest string quartets in world. No ensemble is more apt for such a mission than a string ensemble, that can effortlessly glide between pitches with freedom, at various ranges, and at various speeds. 

In conversation with the composer Michael Seltenreich, he revealed that the idea came to him while thinking about spoken language. He explained that he was fascinated by the incredible amount of information that is conveyed when people speak in form of the pitch contour of their voices, its stability, and its range; all while having nothing to do with the actual pitches themselves. It was this phenomenon that he sought to explore in Trajectories.