Music technology (electric) remained so until the 1920s, when several recent radio-related developments in electronics converged to revolutionize the recording process. These included improved microphones and auxiliary devices such as electronic filters, all dependent on electronic amplification to be of practical use in recording. In 1906, Lee De Forest invented the "Audion" triode vacuum tube, an electronic valve that could amplify weak electrical signals. By 1915, it was in use in long-distance telephone circuits that made conversations between New York and San Francisco practical. Refined versions of this tube were the basis of all electronic sound systems until the commercial introduction of the
David Davies (electrical engineer) David Davies (electrical engineer) Sir David Evan Naunton Davies , known as Den Davies or David "DEN" Davies, (born 1935) is a British electrical engineer and educator. He was knighted for services to science in 1994. 1985-1988: Head of the Department of Electronic and Electrical Engineering at University College London (UCL), and holder of the Pender Chair, having already been lecturing there, in "Communications Systems", for many years prior to that. 1986-1988: Vice-Provost of University College London 1988-1993: Vice Chancellor of Loughborough University 1993–1999: Chief Scientific Adviser for the Ministry of Defence 1994-1995: President of the Institution of Electrical Engineers