Last weekend I played a recital using four different horns (more here, all not my normal horn) and on three different mouthpieces (all not my normal mouthpiece, but mostly with my rim). It was very fun, bucket list type stuff, but there is a consequence to it (and the struggle to play in tune on those four different horns), as subsequently as the week began I could not play in tune on any modern horn!
I have had this experience several times before, developing the topic in fact into a full scale article that was published in The Horn Call 33, no. 3 (May, 2003). The title of that article was “Placing Pitch ‘in the Pocket'” and a version of it has been hidden in my older Horn Articles Online website for years (here).
At that time a central thing I did (that is not actually described in the older article) was develop a personal warm-up routine that was geared specifically toward setting my pitch placement, a topic I am sure some readers will benefit from thinking over and one I personally returned to this week.
Essentially the routine is in four parts. The first step is to warmup briefly on virtually any easy exercise. The point being that your pitch will likely actually be off as you start, and don’t even worry about it. Don’t try to tune, just get gently warmed up. This step will take maybe 3-4 minutes maximum.
Step two involves playing exercises that include a pitch bend. I describe a couple of these in the original article, and at this point today would normally use a shortened version of the beginning of the “Shawarma” exercise in the Brass Gym for horn, which was not in print back in 2003 to be mentioned in that article. The idea at this point in the warmup is to end each of the bending exercises with your best, most resonant sound, again with no reference to a tuner. Focus on how it sounds (don’t use a practice mute!) and feels.
Now that you have optimal sound production established, get out a tuner and see where that best resonant sound actually is. Likely it will be lower than “normal” by a bit. Keep that feel of where the pitch is and tune your main slide so you are in tune at that pitch level.
The final step then is to continue tuning up with basically any routine you would use, maintaining that feeling of centering on your most resonant, beautiful tone. I like using a few more Brass Gym for horn exercises such as “beautiful sounds” with the CD to reinforce pitch level, and I have a few other exercises I like to do with a drone. Feel free to use a tuner to hold pitch, and you may find that some exercises you might use are rather more difficult to hold to pitch than you might expect.
Part of what you want to do here is retrain your ear as well, that you really have the feel for the correct pitch level, not some sharp pitch level that seems right/normal to you (due to repetition or lack of a frame of pitch reference) but is not.
Within a few days of starting a routine of this general type you should feel that your pitch is getting more centered and will be more reliably placed. Good luck!