A clear-cut cessation of sound is not so difficult to obtain as is unanimous attack. The flow of air through the instrument ceases, and the sound ceases also. It is as simple as that! Yet this must be thoughtfully done, or some unwanted effect is likely to crop up. Some players give a final 'kick' to the release; others always cease playing too soon; or, in pianissimo, let the tone and intonation deteriorate. Such unwanted effects are not purposely done, and indeed the player may well be unaware of them, for they are defects that may have psychological causes.
The player can only hear himself in a certain, limited way; the band trainer is there to stand back from the sound-picture, and to control the effect from his more advantageous standpoint.
Precision in release is more difficult to evoke in pianissimo than in louder passages. The orchestral pianissimo which can die away so gradually that listeners cannot really tell when it ceases is an effect almost impossible to obtain from a group of brass players - unless it be in the open air, or a very large hall; but it is an effect devoutly to be desired, and well worth striving for.
It requires absolute control of breathing, and the lip and facial muscles; and a highly developed sense of team work among the players. Teach them to keep all the faculties at attention right until the end of the chord, and indeed for a moment or so afterwards, while the effect carries on as it were in the ensuing silence.
The fortissimo release can be really exciting. In this case the pressure of breath and tone in 'travelling forward' until the final moment. The type of release must then be dictated by the style of the music - it might be merely a sudden cessation of sound, or it might be given a final sforzando effect, by a sudden sharp pressure of the breath.
An interesting experiment can be made by getting the players to effect the release by suddenly pushing the tongue between the teeth. This can give a really precise release, but the method is probably of little practical value.
The conductor must indicate the moment of release very clearly, especially by the use of a preliminary beat, similar to that used to introduce the 'attack'. Once his young and inexperienced players have learned to watch for this, he will have little difficulty in obtaining the effect he wants. this preliminary beat will again take its style from the mood and tonal weight of the music.