Method
By alternating between a note and the same note with an alternate fingering, a slightly-detuned tremolo effect is achieved. This can be varied in tempo and dynamics, and combined with any number of other contemporary techniques.
Necessary information
It is essential that the composer either a) allow for multiple alternatives, given the prevalence of different keys of tuba, or b) write for a specific key of instrument and use the exact fingerings for the given tremolo combination. Either option is preferable, given the aims of the composer. This is not an issue with the euphonium, which uniformly is notated either in C bass clef or Bb treble clef. To determine possible alternative fingerings, please consult the overtone charts from Section 2, under “Range/Harmonic Series”. For instance, on an F tuba, a middle C may be performed on the open bugle/6th partial, on valves 1+2 in the 7th partial, and on both valve 4 and valves 1+3 in the 8th partial. Each fingering produces their own microtonal variant on the note of middle C, and alternating between them can create a variety of tonal shadings.
Notation
This technique can be notated via the use of traditional tremolo notation and a small text prompt describing the technique desired. If a certain key of instrument is being written for, it can be helpful to list the fingerings of the two component notes above the tremolo. If an alternate fingering tremolo is desired but the key of tuba is not specified, the technique can be simply notated without a specific fingering. In this case, the tubist/euphonist will find an alternate fingering that is suitable for the notes requested. This, however, may result in a less than ideal tremolo, depending on the note and key of tuba used.
Relative Difficulty
Beginner to Advanced
Works to consider (bolded titles are particularly representative examples of this technique)
Omaggi e Fantasie – Claude Baker
Five Studies for Tuba Alone – David Reck
Concert Variations – Jan Bach
The Composer's Guide to the Tuba 