All horn players recognize that conductors are a part of the accuracy problem. Gunther Schuller in Horn Technique addresses the topic of accuracy in his section of notes for composers and conductors as follows.
As for conductors, they are well advised to look the other way when a passage includes some delicately placed high notes. If the horn player ‘muffs’ a note, he is at least as sorry as the conductor: he has a lot more at stake. A look of surprise, disdain, or distemper on the conductor’s part will do very little to alleviate the situation. High notes are always a treacherous matter, and if a man misses one occasionally, the conductor should not take it as a personal affront. This is all too often the case, because some conductors have the quaint notion that the modern double-horn player need only to push down his thumb (Bb) valve, and out pop a series of perfect high notes. This actually happened to me quite a few years ago at the Metropolitan with a world-famous ‘maestro’. A few minutes of thought about the position of those notes in the harmonic series (even on the B flat horn) would have revealed to this conductor how eminently silly his remark was.
Ouch! But have to love that quotation, we can all relate.
Fred Fox points to a mental side of accuracy in Essentials of Brass Playing.
The muscles of the embouchure do not change from minute to minute, hour to hour, day to day. If a series of notes are played well and then missed when replayed, the muscles of the embouchure cannot be blamed since they certainly were identical in both playings (assuming no fatigue factor). We must then conclude that the mind which directs the muscles wandered. The mind became careless in its orders! The concentration on precision was lacking.
I feel that there are two types of cracked notes. The big miss where as much as a third above or below comes out, and the close miss, something less than an intentional grace note. The big miss is really not excusable, and I call that a “goof!” It is as bad as aiming at the bull’s-eye of a target and missing the whole target. When that occurs it should not be condoned by the player. He should tell himself there is no excuse for a bad miss or “goof.” …if the “goof” is accepted as part of the inconsistencies of the instrument then the player will probably never rise above that….
There is no such thing as turning the quality of one’s playing off and on! Eternal vigilance!
In the addendum to Essentials of Brass Playing Fox also advocates for being set to play just before you need to play. “Setting in advance will greatly increase the accuracy of attacks on high notes or anywhere else on the instrument.”
Fox explains this idea further with the “note cluster” principle.
Producing notes on a brass instrument is a complex process. There is a tendancy [sic] to worry about each note as it is produced….
On the piano one can play a two octave arpeggio, and if the fingers are set over each note, the same set of notes can be played simultaneously—as a cluster. Similarly, the embouchure should be so poised that it can play any note of a given passage at the snap of a finger. What I have done with my students is to tell them to sustain a note and, at the same time, have ready the note one octave above. I warn them that I plan to cue them unexpectedly and that they are to play the top note instantaneously. Invariably the octave is played flawlessly on cue, it is ready. The whole embouchure seems more in balance when the whole phrase is mentally anticipated.
When the series returns we will have a number of shorter quotes related to accuracy.