3.7 Stray magnetic fields

Stray magnetic fields are the natural enemy of magnetic recordings. The susceptibility of magnetically recorded signals to deterioration up to erasure depends on the coercivity of the magnetic material—the resistance of a given magnetically orientated material to re-orientation. It also depends on the kind of the signal representation, which have varying sensitivity to partial erasure. The most susceptible signal representation is analogue (linear) audio recording. This also occurs on the (analogue) linear audio tracks of video tapes. FM audio, all video, and all digital signal representations are more resistant to distortion caused by magnetic fields. The permissible magnetic field thresholds are, therefore, given for analogue (linear) audio signal representations.