I just wrote this for the Mello Tone thread in the Mellophone forum, and figured it would be a good idea to see how everyone else stands on brass arranging (in the drum corps setting).

Simply put, my philosophy is to treat the drum corps brass ensemble like what it is, a choir. Your trumpets are your soprano voice, your mellophones are an alto/1st tenor, the baritones are a 2nd tenor/baritone, the euphonium is a more solid baritone, and the tuba as the bass voice (treated like a Bass-baritone voice, not a choral bass). You will ocassionally see composers write for alto and soprano in unison, but you never see a decent composer in his right mind writing alto parts that are ridiculous in range, they'll generally drop it at the octave. If you treat the instruments as you would the human voice, you won't have to worry about treating the instruments incorrectly, or requiring the players to use a tone uncharacteristic of the instrument. In short, here's my general arranging philosophy:

• Leads/1st Trumpets - 1st Soprano. They have the entire range of the instrument, though they sound best in the mid to upper range. Never write low parts for them unless they are doubling one or both of the other two trumpets.
• 2nd & 3rd Trumpets - 2nd Soprano. They have the low to mid range of the instrument covered very solidly, and they are often used in unison (either rhythmically or harmonically) with the Leads/1sts. They will ocassionally take on a lower role, but only when looking for a particular timbre.
• Mellophones - Alto/1st Tenor. While they often split on fuller/louder chords into an Alto I/Alto II (Alto/Tenor I) arrangement, they are just as likely to be in unison with each other. When looking for a softer or more gentle setting, their timbre and tone on the low to mid treble range is essential (in this case they would be comparable to the Tenor I section of an all-male chorus). If there is a need for the upper register to sing out, doubling at the octave between Mello I & II will cause the upper octave to sound much louder and fuller, however, if the ensemble is capable of it, a unison upper range is just as good. Be wary with parts that require too bright of a tone to blend with the trumpets, and if this cannot be avoided, make the passage as short as possible.
• Baritones - Tenor II/Baritone I. They provide support for the melody, though they can also take the melody depending on the range and style of writing. It's fairly hard to write a baritone part that's bad for the players' tone. One will often see different arrangers taking their 1st Baritones up into the stratosphere (high Bb range), but on the field, the tone comes across as thin, strained, and just not good in an ensemble setting. While the upper range may be used in solos or small ensembles, as a section, I tend to restrict the baritones to the upper G and lower.
• Euphoniums - Baritone. While they have the same range in all praticality as the baritones, I treat the euphonium as a lower baritone voice for most writing. They will be in unison with the baritones if there's a single line, and this does not do any harm to any voice in the range. If there is an important melody which is split in harmony (though with similar rhythm) within the barieuphs, I'll give the melody to the euphs as they have a richer, fuller sound. On the same token, I often use the euphs to bolster a tuba part at the octave when that extra bass presence is needed. Next to mellophones, the euphoniums are the most useful instrument in multiple situations.
• Tubas - Bass-baritone. While this doesn't exist in the choral setting as a voice, the tubas play the role of a solid, large, low bass voice in a choir. They can be used in their upper register, but when getting to terribly high, I find the tone much more pleasant if you just leave the tubas out and let the euphonium cover the part. Either way, tubas are generally just fun to write for . . . they're just BA in general.

When composing or arranging for a drum corps brass ensemble I generally use 3 Trumpets, 2 Mellophones (often with multiple div. parts), 2 Baritones, 1 Euphonium and 1 Tuba. I'm guilty of doubling the tuba part on euphonium (8va) just for added foundation. Of course a tuba is not a euphonium so there are subtle differences and in the end i consider the euphonium a closer cousin to the baritone. One thing I don't like that composers (Downey) do is have lead trumpets play the entire chord an octave up. Might as well drop the rest of the ensemble and saddle everyone up with trumpets. You have a 60+ piece brass ensemble at your disposal, don't rely on 5 or 6 trumpets and then let everyone else act as filler. This is, obviously, just one man's opinion.

When composing in a drum corps style arrangement, I use 3 trumpets, 2 mellos, 2 baritones (splitting the 2nd baritone to put the harmony of the 3rd and 2nd baritone) and 1 tuba. Finale demo only allows for 8 staves so I work with what I have.

I'm going to start with the alto voices, as I am a mellophone player. With the alto voice, I generally love to give them the color of the ensemble as well as the interesting lines. They can be used to add dimension to the music. I also like to give them the melody in occasion, rather than most people arrangers giving the trumpet the melody 90% and the other 10% is given to the mellos or baritones (or tubas if they're lucky). Mellos are almost always going to play moving lines under the ensemble if the ensemble is playing chords or sustains. Mellos are to be used to add color (as I said before) by creating suspensions and the 7ths and 9ths.

The soprano voices are a bit tricky with me because though I may play high brass, figuring out how high a certain trumpet part should go is a bit troubling to me. In general, I keep the 3rd trumpets in the mid range most of the time. I don't really find use of going below the staff. Maybe it's because I'm a mello player and I'm not used to playing beneath the staff. Anyway, that said, the 2nd trumpets are generally the support of the leads. I put them in the mid to high register range. By that, I mean from usually an A in the staff to about an A above the staff. Speaking of which, 3rd usually plays from space E to about top line F. Well finally the leads. I like to have the leads have the good parts, in lack of a better term. When they have a melody, they HAVE a melody. Whenever they play technical passages, it's either done in harmony with the 2nds and 3rd (which are playing unison) or the other trumpets are sustaining themselves. Occasionally, they will play with the mellos on technical passages. I usually keep them from about a D in the staff to a D above the staff, most of the time, they are above the staff circa A and G.

Starting with the low brass, I'd like to say it's hard to not think of low brass as just the people-who-play-chords-to-support-high-brass. I try to give them an melody every once in a while. Most of the time, it's something different than what has already been done so they'd get some more uniqueness. Otherwise, I have them for the most part. The third baritones (or euphs even though I haven't really encountered that beast yet) were usually an octave above the tubas, though I've started to stray away from that. The tubas are actually the meat of the sound like most people do. However, I am recently trying to use them to create lots of strong passing tones. The tubas are one of the important voices in the ensemble and they should be treated as such. I occasionally give them something technical to add some texture to the music and to not bore them to with long notes that never end.

To comment on ranges, I'll admit to being a Klesch fan-boy.

• Lead/1st Trumpets - As high as they can play with good tone. Depending on the ensemble, this may be a high Bb, or it could be a Triple G. I usually treat the 1sts as one with the Leads, though if an ensemble calls for it, I'll write a third - fifth below the Leads for the 1sts. I usually don't take these below the staff unless it's in unison with the other two trumpet parts.
• 2nd/3rd Trumpets - I generally keep them below the A above the staff. If it's a younger ensemble (even Div I level technique-wise), this may be restricted to the G or F. If it's a really young ensemble, I'll let the 2nds handle up to G and the 3rds up to E. On the low end, I try to keep at or above the C below the staff. If it's a slower passage, or a situation where I think I can get away with it, I'll use down to the A below the staff, but this is rare indeed, and will probably only be on something very "brassy." Anything else can be handled by the mellos, or even baritones, better that low.
• Mellos - Leads don't go above a High C as a generalisation. The mello sounds very thin above High C (though in some contexts, the thin and piercing sound can augment a very full sound in the rest of the ensemble a la the trill at the end of Cavies '04). Seconds is dependant on the ensemble, though assuming the standard Div I line, I won't go above an A above the staff. For all practical purposes, I keep the mellos above the Eb at the bottom of the staff, though I'll go down to the C in some rarer cases. I try to avoid the C# and D whenever possible though, as they tend to have issues with tuning.
• Lead Baris - Up to the G three lines above the staff, down to the A at the bottom of the bass clef. Anything higher or lower and the tone's either too thin or too muddy.
• 2nd Baris/Euphs - These I keep to the F (third space above the bass staff), and with the same bottom range as the Leads. They all begin to sound muddy if taken too low, and there's almost no circumstance under which you'll need the baris playing that low that can't be handled by the tubas splitting.
• Tubas - Tubas are entirely dependant on the ensemble. I've seen the Cavies take it up to the Bb above the bass staff and higher, while I've heard other ensembles take them below a low F. I generally keep the absolute lowest note I write as the F 8vb the F just below the staff (and that's only used in split situation where they would be standing still, like a final chord or something). As far as higher notes, the highest I'll keep the section together without any splitting is the F in the bass staff. I'll go up to the Bb above that is it's a special situation, but it'll either be split, or explicity listed as being only for those who can play it with good tone (and/or a solo).

As a tuba player I would just like to say feel free, no, feel encouraged to write high tuba music. The tuba is a beautiful horn with a very large range. From Bb 15vb from Bb (2nd line) to Bb 8va (Bb space above staff). Too many composers hesitate to write tough music for tubas because a few incapable ensembles with poor tuba lines have ruined the image of a good tuba line. I'm not saying we need to be doing 32 note runs at 200bpm through the entire range of the tuba, but would it hurt to throw us a bone once in a while?