Alto trumpet
A valve trumpet in a lower, alto-like range, usually pitched in B♭.
What it means
The term alto trumpet refers to a valve trumpet in a lower, alto-like range. August Reissmann's Handlexikon der Tonkunst of 1882 defines it simply as “a valve trumpet in B♭,” placing it historically within the broad family of B♭-pitched brass instruments.
The name transfers the alto voice designation known from choral singing onto a brass instrument: it refers to a trumpet whose tone color and pitch range are set darker and lower than the higher, more common trumpet.
Musical use
The term alto trumpet appears mainly in older, mostly German-language music dictionaries of the nineteenth century, while it has not established itself as a distinct, widely used instrument designation in modern orchestral practice.
In practice, the field of lower-pitched trumpet instruments overlaps with terms such as bass trumpet: both describe trumpet designs built for a lower range than the standard trumpet, without the terminology having remained consistent across the centuries.
Performance practice
If you encounter the term alto trumpet in historical sources or scores, check the specific pitch and range of the intended instrument when in doubt, since the term has not always been used consistently. For practical performance, a standard B♭ trumpet or, if needed, a bass trumpet usually suffices, depending on the required range.