A friend just sent me a note on an earlier post, and he mentioned that he is writing a lot for brass band. I love the sound of a brass band, and I've wanted to find my mojo to write for that ensemble. But I can't seem to do that, and it got me to thinking about why.
I was fortunate to have done my undergraduate study at the University of Denver. I was one of only two tuba players in the program which meant a lot of chop time. DU does not have a football program so there was no marching band, and there was no symphonic or concert band. Instead, there was a top notch orchestra, and an excellent wind ensemble comprising mostly graduate students, under the expert direction of Joe Docksey. Joe was a musical purist, and a champion of the one-on-a-part wind ensemble concept; this ideology became deeply ingrained. It's also when/where I fell in love with Grainger's music - a subject for another day.
Starting out writing mostly quintet charts, by the time I had written twenty or so, I had gotten pretty good at making the necessary compromises to make a quintet sing. So the first time I wrote something for brass ensemble, I remember feeling overwhelmed with the thought "what in the hell are you supposed to do with all of these brass players?" Being one to turn challenges into opportunities, it occurred to me that not everyone needed to play all the time (a habit learned from my quintet pedigree), and that writing for brass ensemble opened up possibilities for nearly endless color combinations (duh).
I used to watch a few shows on Food Network - Alton Brown is a favorite. AB likes to say "don't add anything that doesn't bring some flavor" or something like that. He was referring to adding water vs. some other liquid to a recipe.
So I rarely write unisons. When I do, it's even more rare for it to be the same instrument (e.g. two tenor trombones or two B flat trumpets) - to me, that's an opportunity missed to color a sound in a slightly different way. Horn and trombone in unison have a different color than 2 tenor trombones - even mixing the sound of a bass trombone with tenor trombone changes the color. That's not to say that it never happens in my charts, but it's never just because. It has to serve either a balance or color concern, or solve a voice leading problem.
Other than that, it's pretty much one on a part.