This composition was commissioned in 1976 by the Composers Authors and Publishers Assocation of Canada (CAPAC) with the assistance of the Canada Council. The world première took place November 19, 1977 in the "Kultur Forum Center" in Bonn, Germany. The Canadian Brass premièred the work, which was at the time titled Improvisations, and in December of the same year, gave its Canadian première in Toronto. This performance was heard the following year on the Canadian Broadcasting Corporation.

It has since become one of the most frequently performed works for brass quintet not only in Canada, but also by prominent foreign ensembles, including the New York Brass Quintet, the Wisconsin Brass Quintet and the English Brass Ensemble.

Morawetz derives most of this Sonata's colours and rhythmic drive from a polyphonic texture which in some ways are comparable to string quartet writing. Therefore he achieves sounds which in many respects are quite different from most compositions written for this medium.

The first movement is very rhythmic and contrapuntal in character. Structurally it is free in form but achieves strong unity by reappearance of all the main themes in the second half of the movement, though considerably changed in colour and texture.

The second movement starts with an impressionistic colour: a short, staccato five-note figure in the muted first trumpet picturing falling raindrops accompanies the melancholic melody of the second trumpet, which reminds one of the drowsy mood of a misty day. This rather impressionistic mood of the beginning builds a strong contrast to the expressive feeling of the middle section, which starts with a melody in the low register of the horn. It gradually increases in volume and is later continued by a new melodic line in the 1st trumpet which leads the music to a dynamic and emotional climax. At this point the melody is once again taken over by the horn which leads it back to the impressionistic mood and colour of the beginning. This time all five instruments enter with mutes and in the last seven bars a duet between the trombone and the tuba takes over the "rain drops" accompanying figure. The low dark register of the tuba ends the movement in a sombre mood.

The third movement is a lively Allegro which could be called "Toccata for Brass" considering the robust rhythms and great deal of vivid motion alternating from one instrument to the other. In the concluding coda, agitated triplets replace the previously prevailing 16th notes. The agitated excitement grows steadily until a slightly slower and heavier tempo in the last four bars brings the movement to a climactic ending.