each note in the harmonic series can be lowered by an interval of up to a tritone. The lowest note of the standard instrument is therefore an E – a tritone below B. Most experienced trombonists can play lower "falset" notes and much lower pedal notes (first partials or fundamentals, which have a peculiar metallic rumbling sound). Slide positions are subject to adjustment, compensating for imperfections in the tuning of different harmonics. The fifth partial is rather flat on most trombones and usually requires a minute shortening of the slide position to compensate; other small adjustments are also normally required throughout the range. Trombonists make frequent use of alternate positions to minimize slide movement in rapid passages; for instance, B3 may be played in first or fifth position. Alternate positions are also needed to allow a player to produce a glissando to or from a higher note on the same partial. While the lowest note of the tenor trombone's range (excluding fundamentals or pedal notes) is E2, the trombone's upper range is theoretically open-ended. The practical top of the range is sometimes considered to be F5, or more conservatively D5. The range of the C tenor trombone is F2 to G5. 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. Soprano trombone The soprano trombone is usually pitched in B an octave above the tenor, and has seldom been used since its first known appearance in 1677 outside of trombone choirs in Moravian Church music. Built with mouthpiece, bore and bell dimensions similar to the B trumpet, it tends to be played by trumpet players. During the 20th century some soprano trombones—dubbed slide cornets—were made as novelties or for