A soprano trombone is a treble instrument in the brass family. Similar to other trombones, the soprano trombone features a slide mechanism by which the player can alter the pitches produced during performance. The soprano trombone is smaller and higher in pitch, however, and is not as common as larger trombones with lower ranges.
In terms of size, soprano trombones are similar to trumpets. In fact, the bell is usually the same size as the Bb trumpet. The instruments also use the same mouthpiece, so usually trumpet players play the soprano trombone because of the embouchure or mouth shape and position requirements. The soprano trombone is not the smallest member of the trombone family, however. The sopranino and piccolo trombones are smaller, pitched in Eb one octave above the alto trombone and in Bb one octave above the soprano trombone, respectively.
The range of the soprano trombone is similar to the Bb trumpet, as well. The low end of the range is around E3, while the upper range is roughly C6. The exact range limitations depend on the performer's ability to control his embouchure and the slide positions to navigate through the harmonic overtone series. It is not unusual — and is even expected — for more advanced players to have larger ranges than beginners.
Similar to other trombones, the soprano has seven positions for the slide. Players combine these positions with manipulation of the embouchure to get all the notes of the chromatic scale. The fact that the instrument is roughly half the size of a tenor trombone means that the distance the player must move between positions also is half as big, which throws some performers used to reaching for positions on the tenor.
The similarities between the soprano trombone and the trumpet result in some people referring to the soprano trombone as a "slide trumpet." This is not entirely accurate. The true slide trumpet was a historical instrument common in England in the 19th century, having only three positions instead of the seven positions the soprano trombone has.
Although soprano trombones sometimes are found in trombone choirs or as a solo instrument, they are more of a novelty. This is largely because they are more difficult to keep in tune than their larger counterparts. Some players have used the instrument with great success in jazz, however, because the slide allows the performer to execute true glissandos, moving seamlessly from one pitch to another in a way that is not truly possible on the trumpet.