ABitRusty said
 

I didnt know about these Andrew.   So Im understanding youll play an already composed piece then have a solo?.   The solo youre working on is what youve shared here?  

  

Hmm, maybe I should explain a little more of what's going on.

The piece is a viola concerto, so the whole thing is for solo viola accompanied by orchestra.

In many concertos, including this one, there's at least one spot called a cadenza where the orchestra drops out completely and leaves the soloist to play unaccompanied for a while. This is really a chance for the soloist to show off without being interrupted by the orchestra at all. Traditionally soloists have written or improvised their own cadenzas, though over time it became more and more common for composers to write out the cadenzas in full, and with some concertos a particular soloist's cadenza has been adopted by many other soloists (such as Joseph Joachim's cadenza for the Brahms violin concerto). The Hoffmeister viola concerto has cadenzas indicated at the ends of the first and second movements; Hoffmeister did not write the cadenzas himself but left them to the soloist.

As for the actual content: the cadenza is a short, virtuosic fantasy on musical material found in the concerto movement, typically somewhere between 45 and 90 seconds in length. I've taken musical motifs from various places in the first movement of the concerto, recombined them, and embellished some of them.

At the very end of the cadenza, a long trill on the second step of the scale is traditional, especially for music from the Classical era. Because the length of the cadenza is up to the soloist, the long trill is as a signal to the conductor and the orchestra that the cadenza is ending and they should be ready to come back in on the next note.