Read Back Signals in Magnetic Recording - Research Group Fidler

Introduction
1 IntroductionEquation Section 1
The idea to use magnetism for recording originates from Oberlin Smith (1840-1926), an
inventor, industrialist, and mechanical engineer. His idea based on a visit to Thomas Edison’s
laboratory in 1878. Lacking time to pursue further development - it is not known whether he
built a working device - he published a description of magnetic recording in Electrical World,
Sep. 8, 1888 [1]. Figure 1.1 shows the original drawing of Oberlin Smith. It demonstrates the
basic principle of magnetic audio recording used up to now. The audio waves are transformed
by the microphone (A) into an electrical signal and are recorded in the form of magnetization
patterns on a string covered with iron filings (C), passing through an electromagnet (B). To
reduce noise a battery (F) supplies bias current. The string is moved from the supply reel (D)
to the take up reel (E).
Probably inspired by Oberlin Smith’s article Valdemar Poulson built the first working
magnetic recording device (see Figure 1.1). He used an inductive head moving over a wire
wrapped drum. In the following decades a lot of improvements were invented, but as
information carrier mainly wire wrapped drums were used. Later tapes coated with magnetic
powder replaced them.
Figure 1.1: The original drawing of Oberlin Smith (1888) and Valdemar Poulson’s
telegraphone [2].
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