Bias increases the signal quality of most audio recordings significantly by pushing the signal into more linear zones of the tape's magnetic transfer function. == History == Magnetic recording was proposed as early as 1878 by Oberlin Smith, who on 4 October 1878 filed, with the U.S.
patent office, a caveat regarding the magnetic recording of sound and who published his ideas on the subject in the 8 September 1888 issue of The Electrical World as "Some possible forms of phonograph".
By 1898, Valdemar Poulsen had demonstrated a magnetic recorder and proposed magnetic tape.
Carpenter in 1921, eventually resulting in a patent in 1927.
Carpenter in 1921, eventually resulting in a patent in 1927.
Fritz Pfleumer was granted a German patent for a non-magnetic "Sound recording carrier" with a magnetic coating, on 1 January 1928, but it was later overturned in favour of an earlier US patent by Joseph A.
The first rediscovery seems to have been by Dean Wooldrige at Bell Telephone Laboratories, around 1937, but the BTL lawyers found the original patent, and 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.
The first rediscovery seems to have been by Dean Wooldrige at Bell Telephone Laboratories, around 1937, but the BTL lawyers found the original patent, and 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.
The first rediscovery seems to have been by Dean Wooldrige at Bell Telephone Laboratories, around 1937, but the BTL lawyers found the original patent, and 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).
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).
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).
After the war, Boosey and Hawkes also produced a "Reporter" tape recorder in the early 1950s using magnetic tape, rather than wire, which was based on German wartime technology. == Theory == As the tape leaves the trailing edge of the gap in the tape head, the oscillating magnetic field due to the applied AC bias is rapidly reduced to the average magnetic field of the much slower-changing audio signal, and the tape particles are therefore left in this magnetic condition.
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