Thanks for the link Steve!
I think it would have still been acoustic recording at that point. The clips sound like it. A small, loud combo like that was probably one of the better things to record at that point because all the horns at least came through clearly and the clarinet very much so.
Sounds as if there might have been a bass horn as well as the trumpet and trombone.
Piano is just barely there, but probably better than those early blues recordings trying to capture an acoustic guitar.
I remember that peculiar early "Jass" spelling. I actually think I might have a recording by them - unless that was common to the early era. I do have a few 78s that go back that far.