Modulation noise in thin-film metallic media: elements of pulse/transition modulation theory

Density limits imposed by the microstructure of magnetic recording media

“…In the bits themselves the magnetization of all grains is either 'up'' or ''down'' and there is no statistical freedom left, and hence the bits are noise free. Then it can be shown that the SNR is proportional to B/s n [8][9][10]; one can also say that the recording is dominated by the transition noise. Inspecting Eq.…”

“…However, Minhuin has pointed out that the additive magnetization noise is converted into various types of modulation noise during the read-back process [9]. The most prominent modulation effect is what Minhuin had called ''pulse shift modulation'', which is somewhat imprecisely often equated to transition jitter.…”

“…The read-back process represents a band-pass filter, which in particular does not pass high frequencies, due to the various loss mechanisms, such as spacing loss and gap loss [8]. It is clear that the spatial frequencies associated with these gaps must be very high and consequently the (noise) side bands caused by the modulation are heavily distorted at readback [9]. In a somewhat simplified way, one can say that the readback process inherently suppresses the high-frequency portions of the medium noise.…”