Basics of software-defined radios and practical applications

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For the indie band, see The Microphones. Several different types of microphone are in use, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. In order to speak to larger groups of people, a need arose to increase the volume of the human voice. The earliest devices used to achieve this were acoustic megaphones.

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Some of the first examples, from fifth century BC Greece, were theater masks with horn-shaped mouth openings that acoustically amplified the voice of actors in amphitheatres. German inventor Johann Philipp Reis designed an early sound transmitter that used a metallic strip attached to a vibrating membrane that would produce intermittent current. David Edward Hughes invented a carbon microphone in the 1870s. This was independently developed by David Edward Hughes in England and Emile Berliner and Thomas Edison in the US. Jack Brown interviews Humphrey Bogart and Lauren Bacall for broadcast to troops overseas during World War II. Wente of Western Electric developed the next breakthrough with the first condenser microphone.

In 1923, the first practical moving coil microphone was built. The Marconi-Sykes magnetophone, developed by Captain H. Round, became the standard for BBC studios in London. Also in 1923, the ribbon microphone was introduced, another electromagnetic type, believed to have been developed by Harry F.

Olson, who essentially reverse-engineered a ribbon speaker. During the second half of 20th century development advanced quickly with the Shure Brothers bringing out the SM58 and SM57. The latest research developments include the use of fibre optics, lasers and interferometers. The sensitive transducer element of a microphone is called its element or capsule. Sound is first converted to mechanical motion by means of a diaphragm, the motion of which is then converted to an electrical signal.