Businesses in the electronic instruments category supply instruments that create, process or control sound using electronic technology. Typical products include electronic keyboards and digital pianos, synthesisers, samplers, drum machines, electronic drum kits, rhythm units and MIDI controllers. Some suppliers also stock studio equipment such as audio interfaces, signal processors and monitor speakers, although these may be listed separately by businesses focused on recording equipment. Customers may be able to buy new or pre-owned instruments, accessories and replacement parts, including stands, pedals, power supplies, cables and instrument cases. Depending on the business, services can include product demonstrations, advice on choosing equipment, delivery, setup, servicing and repairs. Specialist technicians may diagnose faults, replace components, restore older instruments or help connect instruments to computers and other audio equipment.