<hardware, audio> Any electromechanical device designed to convert sound into an electrical signal. A microphone converts an acoustic waveform consisting of alternating high and low air pressure travelling through the air into a voltage. To do this it uses some kind of pressure or movement sensor. The simplest kind of microphone is actually very similar in construction to a loudspeaker. The analogue electrical signal can be fed into a computer's sound card where it is amplified and sampled to convert it into a digital waveform for storage or transmission. (2002-11-04)

An apparatus which includes a contact of variable resistance; such resistance can be varied in amount by slight vibrations, such as those produced by sound waves. The apparatus in use forms part of a circuit including a telephone and current generator. As the contact is varied the resistance of the circuit and consequently the current intensity changes and sounds are emitted by the telephone corresponding to such changes. If the microphone is spoken to, the telephone will emit corresponding sounds, reproducing the voice. It has been found in practice that carbon gives the best microphone contact. One of the simplest and earliest forms is shown in the cut. A short rod or pencil of carbon, A, such as used in batteries, is sharpened at the ends and rests loosely in a vertical position between two blocks of carbon, C C, in each of which a hole is drilled to receive one of the points. The blocks are carried on a standard and base D. The blocks are connected with two terminals x, y, of a circuit, including a telephone and battery. There are two contacts to be disturbed. If delicately adjusted a fly walking over the base-board will disturb the contacts enough to produce sounds in the telephone. These sounds are possibly not due only to sound waves, but in part to absolute mechanical disturbances. The various forms of telephone transmitter are generally microphones. Fig. 242. MICROPHONE.