Comment by erikness
3 hours ago
But you'd only adjust the position of that A if the band is playing an F major chord. Only then.
The D in 1st position - it varies from horn to horn but more often than not yes it'll be a little flat. If you're playing the D as the third of a Bb major chord, then you're already adjusted, easy. If you need a really in-tune D, either 1) tune the whole horn such that 1st position is not quite "all the way in" so you have some room to sharpen the D, 2) use the D in 4th position instead.
Lowering the thirds of chords when you're playing them is generally not something people worry about until they're serious players. And it's really more of an ear training thing than a neuroticism thing. The exercise is to play a static drone over some speakers (say a D), and then play each note of a D major chord up the range, sliding in an out until you can sort of feel the overtones locking in. On the F# you'll feel the lock-in at a flatter position that F# normally is. And the idea is that this proprioceptive sense of intonation will then carry over to your playing.
I guess high school teachers can get away with mentioning the A as a global rule simply because high school music rarely has a key with sharps. You're usually playing in a key that uses A-flat instead of A, or it's the third on an F or the sixth on a C or a seventh on a B-flat. Playing that sixth a little sharp might or might not be wrong, but it's unlikely to be a held note of a chord in high school repertoire. The seventh might be part of a chord, but that's going to be pretty crunchy for high school curricula.