Reproduce system noise in wide-band magnetic recording systems

Noise in a magnetic recording system can be introduced in the recording process, the reproducing process, or by the media itself. Recording noise is generated mainly by record head-to-media spacing variations. Media noise is generated by the particulate nature of the media as well as gross inhomogenities in the media. Reproduce noise is generated by the reproduce head, the reproduce amplifier, as well as reproduce head-to-media spacing variations. This paper will deal only with the noise in the reproduce head and amplifier. The reproduce head, which can be considered as a passive circuit element, will generate noise referred to as thermal or Johnson noise. The amplifier, which is an active circuit element, will generate both shot noise and thermal noise. In addition, flicker or noise will prevail at low frequencies. In the case of transistor amplifiers, the generated amplifier noise will be a function of the head impedance. Hence, the design of the reproduce system must be considered as a unit, if the optimum signal-to-noise ratio is to be achieved. The noise generated by the reproduce head is a function of the electrical losses in the head material and the geometric design of the head. A knowledge of the material complex permeability and the geometry of the head is essential for predicting the noise behavior of the head. Knowing the reproduce amplifier circuit parameters, the complex permeability, and geometry of the head, it is possible to predict the signal-to-noise ratio of the system. Typical calculation of the signal-to-noise ratio of both wide-band and narrow-band systems have been carried out.