TLDR: we have to play in tune and I am sharing some exercises and resources to help get better at it
Intonation can be tricky on an instrument that has so many slides. I very often am asked by students “how do I tune my horn?” The easiest way to start is to tune the F horn to the B flat horn (if the horn is a double). I will play notes that both sides of the horn share such as A or A flat. Both notes exist with and without the trigger (thumb valve) and I can compare pitch. The horn needs to be tuned within the general pitch center of the ensemble.
Things get more difficult to explain because simply tuning the instrument to itself and then to a tuner set at A=440, isn’t enough. And I argue, largely unuseful.
Every note I play belongs to a greater harmonic structure. And since I only play one note at a time, I have to figure out how I relate to the harmonic structure. In other words, am I playing tonic? the 5th? a minor 3rd? Learning what to do, how to do it, and how far to take it is crucial to the ability to “play in tune.” If I don’t adjust to the pitch center and sit oblivious to my surroundings is unacceptable.
However, many times students know they’re out of tune - just not what to do about it because the moments can be so fleeting.
Here are some things to try first:
Push all of your slides in (hopefully they won’t get stuck! if your horn is not clean, only push in as far as they’ll go, but get your horn cleaned professionally)
tune both sides of the horn to each other (read on)
tune open partials like C’s and G’s - knowing that this can’t be a perfect science because the inherent slide length creates different ratios of length as valves are depressed
tune the 1st slides, 2nd slides, etc to each other remembering that the more valves you depress (i.e. 12, 23, 13, 123) the more “out of tune” the instrument is, or the further away from the base length
be mindful of hand position, the sound should never be compromised (too stuffy, too abrasively bright) by intonation
there are other very important things that influence pitch: oral cavity (vowels, tongue position), mouthpiece pressure (the more pressure on the upper lip, the higher your pitch is likely to go), air stream and lack of air support, “chewing” the note from lack of corner support (also known as “twa-twa”)