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 non-linear response of magnetic tape at low field strengths. In 1940, J. von Braunmuhl and Dr. W. Weber discovered (accidentally) that the addition of a high-frequency tone kept the recorded signal in the linear-response zone, resulting in a striking quality improvement.