  This report is aimed at reviving the explanation of flicker-noise
observations as the result of spectral measurement of very low-frequency but
stationary narrow-band fluctuations named as infralow-frequency noise (ILF
noise) [A. Ya. Shul'man. Sov. Tech. Phys. Lett. 7, 337 (1981), Sov. Phys. JETP
54, 420 (1981)]. Such a kind of the spectrum analyzer output takes place when
the ILF-noise correlation time is much longer than the analyzer reciprocal
bandwidth. This result is valid for both analog and digital spectral
measurements. The measured signal is proportional in this case to the mean
square and not to the spectral density of the noise. The equilibrium
temperature fluctuations and the defect-motion as mechanisms of $1/f$ noise in
metal films are reconsidered from this point of view. It is shown that the
ILF-noise approach allows to remove the main objection against temperature
fluctuation model and difficulties within the defect-motion model widely
discussed in literature.
