Improvement of recording density by means of cosine equalizer

Waveform compensation by cosine equalizer, which is simple in composition, was applied to digital magnetic recording in order to improve recording density. The equalizer is composed of a delay line with delay constant τ, an amplitude divider with dividing ratio K and a differential amplifier. There are optimum combinations of K and τ to obtain minimum pulse width with minimum amplitude reduction. Half pulse width was found to be reduced to about 0.6, with an optimum combination of K and τ. This means that an effective increase of recording density by about 60% or more is obtained. Pulse crowding is reduced in accordance with the reduction of the half width of an isolated pulse. However, it was found that practicable increase of the recording density is reduced to about 30%, as an example, when signal-to-noise ratio (SNR) at the input is 35 dB. In case of a lower SNR, the recording density limit is rather decreased, when level sensing is applied as a signal detection method.