Tape bias

Tape bias is a high-frequency signal (generally around 100 kHz) added to an input signal when it is recorded by an analog tape recorder. Tape bias increases the signal quality of most audio recordings significantly compared to unbiased recordings.

Early tape recorders simply applied the unadulterated input signal to the record head, resulting in mediocre recordings with poor low-frequency response. This is largely due to the nonlinear response of magnetic tape at low field strengths. In 1940, J. von Braunmühl and Dr. W. Weber accidentally discovered that the addition of a high-frequency tone kept the recorded signal in the linear response zone, resulting in a striking quality improvement.

External links:

• http://hyperphysics.phy-astr.gsu.edu/hbase/audio/bias.html