A theoretical and experimental investigation is made into the mechanism of noise in magnetic media as used in magnetic recording. It is shown that the basic noise in a wow and flutter free system arises from the fact that the domain size in metals or the particle size of oxides is finite, and improvement in the lower limit of noise can only be made by reduction of particle or domain size. The effect of impressed ac and dc magnetization on the noise level is also examined.A theoretical value for the tape noise arising from the particle nature of an oxide medium has been derived by taking into account the modern theories of magnetism of the iron oxides and evaluating exactly the mathematical functionf(x) which appears in the noise equation. Good agreement with the observed noise voltage is obtained.It is also shown that the basic wide‐band unmagnetized tape noise level of 0.6 μv for the head employed is extremely low and that for the ideal system the theoretical signal/wide‐band unmagnetized tape noise ratio is independent of tape velocity and varies as the square root of the track width.