A microphone is an acoustic-to-electric transducer or sensor that converts sound in air into an electrical signal.

Microphones are used in many applications such as telephones, hearing aids, public address systems, film production, radio and television broadcasting, in computers and for non-acoustic purposes such as ultrasonic checking. Most microphones today use electromagnetic induction (dynamic microphones), capacitance change (condenser microphones) or piezoelectricity (piezoelectric microphones) to produce an electrical signal from air pressure variations. Microphones typically need to be connected to a preamplifier before the signal can be amplified with an audio power amplifier or recorded.


This is a Travel-Master Dictaphone made in the 1960s, which uses Dictabelt technology and comes with a separate external microphone. Dictaphone is a trademark, but the term has become genericized to refer to any dictation machine.

Dictaphone introduced Dictabelt in 1947 having relied on wax-cylinder recording up to that point. The plastic belt was loaded onto a pair of metal cylinders and rotated before a blunt stylus recorded the audio signal by impressing a groove into the plastic rather than engraving the plastic.

This Dictaphone was presented to The Earl Mountbatten of Burma in 1965 on the occasion of his being made an Honorary Member of the Institution of Electronic and Radio Engineers.