A<unk>  is a device designed to improve<unk>  by making sound audible to a person with<unk>  loss.<unk> s are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers such as PSAPs or other plain sound reinforcing systems cannot be sold as<unk> s". Early devices, such as ear trumpets or ear horns, were passive amplification cones designed to gather sound energy and direct it into the ear canal. Modern devices are computerised electroacoustic systems that transform environmental sound to make it audible, according to audiometrical and cognitive rules. Modern devices also utilize sophisticated digital signal processing to try and improve speech intelligibility and comfort for the user. Such signal processing includes feedback management, wide dynamic range compression, directionality, frequency lowering, and noise reduction. Modern<unk> s require configuration to match the<unk>  loss, physical features, and lifestyle of the wearer. The<unk>  is fitted to the most recent audiogram and is programmed by frequency. This process is called "fitting" and is performed by a Doctor of Audiology, also called an audiologist (AuD), or by a<unk>  Instrument Specialist (HIS). The amount of benefit a<unk>  delivers depends in large part on the quality of its fitting. Almost all<unk> s in use in the US are digital<unk> s. Devices similar to<unk> s include the osseointegrated auditory prosthesis (formerly called the bone-anchored<unk>  and cochlear implant.
Hearing aid
Vision therapy
Voice prosthesis
Craniofacial prosthesis
Vision rehabilitation
Visual prosthesis
Audio therapy
Aural rehabilitation