The value of AC bias was somewhat masked by the primitive state of other aspects of magnetic recording, however, and Carlson and Carpenter's achievement was largely ignored. The first rediscovery seems to have been by Dean Wooldrige at Bell Telephone Laboratories, around 1937, but their lawyers found the original patent, and Bell simply kept silent about their rediscovery of AC bias. Teiji Igarashi, Makoto Ishikawa, and Kenzo Nagai of Japan published a paper on AC biasing in 1938 and received a Japanese patent in 1940. Marvin Camras (USA) also rediscovered high-frequency (AC) bias independently in 1941 and received a patent in 1944. The reduction in distortion and noise provided by AC bias was rediscovered in 1940 by Walter Weber while working at the Reichs-Rundfunk-Gesellschaft (RRG). Theory A quantitative explanation of AC bias has been given by Bertram. See also Barkhausen effect Dither Hysteresis References Further reading External links Biasing in Tape Recording Audio storage Tape recording de:Tonband#Vormagnetisierung