Musical groups from symphony orchestras to jazz bands usually produce melodies through a blending of many different musical parts or instruments. At times, however, a piece of music will call for a single musician, such as a trumpet player, to assume the musical focus of the composition and carry the melody alone. Such trumpet solos can take the form of playing music that the composer wrote, or the trumpet player improvising his part.
In classical music and other formal orchestral compositions, trumpet solos are usually written by the composer to put a special emphasis on the sound of a single trumpet. This could take the form of a unique melody the audience has not yet heard, or the central melody of a piece. These solos present a challenge for the rest of the musical group because the other musicians must play at just the right volume so that the audience can hear the full composition, but still allow the single trumpet to be heard above all. The rest of the players may play softly in the background to accentuate the trumpet piece, or the composer may juxtapose the trumpet solo with a counter melody performed by the rest of the orchestra.
Trumpet solos in jazz arrangements can take a similarly predetermined form, or can call for the musician to improvise his performance. In this genre, improvisation is also called 'soloing.' If the solo calls for this, then the composer typically writes out only the background he wants the rest of the band to play. The sheet music for the trumpet solo is then simply marked by the musical key signature in which he needs to improvise.
Improvised trumpet solos must work within the key signature the composer marked so that this portion of music works with the music written for the rest of the band. For this reason, the soloist must have a strong command of the different key signatures, knowing exactly which notes are in each one. This not only ensures that the musician does not play off-key during the trumpet solo, but also helps him to use the attributes of each key to improvise more interesting music.
These kinds of improvised trumpet solos can also take the form of solo duels. This usually takes the form of a piano or standing bass playing a background in a particular key, and two or more trumpet players taking turns trying to improvise a more impressive solo than their opponents. These are frequently done in front of crowds, with the magnitude of the crowd's applause used as a scoring system. Alternatively, trumpet players can meet up, without a crowd looking on, and take turns soloing among themselves.