A microphone is a device which allows sound to be amplified or recorded. This is achieved through a process called transduction, the conversion of acoustic sound waves into electrical energy. Early microphones were developed in the late 19th century using carbon and magnetic diaphragms and were used in various telephone designs. The first electric microphones were simultaneously developed in the mid 1920s by Bell Laboratories in the US and Telefunken and AKG in Europe. These new electric microphones produced a much better sound quality and had become standard pieces of equipment in the film and radio industries by the early 1930s.
The introduction of the electric microphone had a fundamental effect upon popular music. In terms of clarity and quality of sound, the standard of recordings improved greatly and the placement of multiple microphones to record individual instruments allowed for much greater control over the mixing of sound levels in a final recording. The microphone also had a significant effect upon performing style both live and on recordings. Famously many singers of the 1930s and 1940s began to tailor their singing styles around the subtleties afforded by the microphone. Crooners such as Bing Crosby and Whispering Jack Smith, torch singers such as Ruth Etting and jazz vocalists such Billie Holiday moved away from the formal sound of trained singers towards a more natural sound, which has been prominent in most subsequent popular music genres.
John Potter (2003: 125) points to various vocal techniques that were made possible by the microphone: a wide dynamic (volume) range; the use of non-vocal, emotional effects (such as sighing or breathing); subtle, throwaway asides and other 'small chromatic inflections' (ibid.); and not having to distort vowels and syllables from speech in order to project them (as is common in classical singing, for instance). Negus (1992: 24) credits Bing Crosby's use of the microphone and new recording technologies as being central in his emergence as the first modern pop star.
The use of such techniques had a clear effect upon the relationship between the performer and the audience. As Will Straw (2003: 158) argues, the microphone's ability to capture the subtlest features of the voice meant that listeners could feel in a more intimate relationship with the singer, building the sense that "audiences had access to the 'real' thoughts and feelings of performers". The profound effect of the microphone and its presence in almost all areas of both recording and live performance continues to this day, to the extent that its effects are no longer regarded as noteworthy by critics and audiences., The microphone has become, as Paul Théberge (2003: 246) puts it, "naturalised and its effects rendered invisible": that is to say, we don't notice it because it is everywhere. This fact only goes to reinforce "the profound impact microphones have on people's experience of popular music".