A bass trumpet is an instrument pitched one octave below trumpet. It uses a trombone mouthpiece and is built in the key of Bb. Like trombone (also built in Bb) it reads music written in the bass clef. It also reads music in Bb treble clef, transposing down an interval of a ninth. The range of the bass trumpet is the same as tenor trombone: concert E one ledger line below the bass clef staff to (conservatively) concert D two ledger lines above the treble cleft staff.