Albin Frehse was a professional horn player and teacher to many of the modern er'a most famous brass players. In his older age he moved to composition where he wrote extensively for brass pedagogy and performance works (including multiple concertos).
These duets are fun to play and get progressively more difficult. These are not recommended for all treble clef brass as the second part often goes down into the bass clef. Grab you horn and give some samples a try to the left, then grab an immediate PDF download above.