structural:reformatting
Alto trombone

The alto trombone is smaller than the tenor trombone and almost always pitched in E♭ a fourth higher than the tenor, although examples pitched in F are occasionally found. Modern instruments are sometimes fitted with a valve to lower the pitch, either by a semitone to D (known as a "trill" valve), or by a fourth into B♭. The alto trombone was commonly used in the 16th to the 18th centuries in church music to strengthen the alto voice, particularly in the Mass. Early 19th century composers such as Beethoven, Brahms, and Schumann began writing for alto trombone in their symphonies, but the subsequent use and popularity of tenor trombones in the orchestra largely eclipsed their use until a modern revival that began in the late 20th century.