Digital hearing aid. This electronic device, designed to receive, amplify and transmit sounds, is used by those who are deaf or hard of hearing. The mould (upper left) fits in the outer ear, with the electronics (lower right, brown casing) amplifying the sounds received by the microphone. The casing includes a battery to provide power, and switches to control the volume and change the digital programming. Digital hearing aids (widely available in the early 21st century) allow the audio processing and output to be controlled and programmed, something not possible with analogue hearing aids.