"Canzon Primi Toni à 8" is from Gabrieli's Sacrae Symphonia, and is in G Dorian mode. It is for two choirs, SATB in each. These ensembles would be seated across from each other in the choir lofts at St. Mark, creating a marvelous “stereo” effect.
The piece begins with the standard canzon motif of long-short-short (the so-called dactyl pattern). The choirs sometimes engage in a call-and-response with each other, and sometimes play together. Most of the phrases are begun with the dactyl pattern, sometimes in diminution.
The Sacrae Symphonia is a collection of: 45 motets for 6, 7, 8, 10, 12, 14, 15 or 16 voices; 14 canzonas in 8, 10, 12 or 15 musical lines; and two sonatas, one in 8 musical lines, the other in 12. It was such a popular publication that many young composers from the north came to Venice to study and brought Italian Baroque style back with them to Germany and other important centers of music.
The source for this arrangement is in volume 10 of the collected works of Giovanni Gabrieli, edited by Richard Charteris.