Mechanical or electronic devices, ''other than instruments'', constructed to create or aid in the creation of musical sounds ... hardware sequencers (or devices which incorporate them) for example, the "stomp boxes" popular with guitarists, "loopers" used for
Live looping, samplers ....
In other words, ''things'' which a musician might buy to enable or enhance a live performance, as opposed to gear designed for production.
Most stand-alone musical instruments probably belong in
:Musical instruments. Some synthesizers, though, have features that fit this category.
Audio electronics