Noise reducing circuit for magnetic recording - allows reduction between 20 and 60 db. and uses compression and expansion techniques

摘要

The circuit arrangement provides a 20db to 60db reduction in the noise levels incurred in electrical signals during magnetic recording particularly but due to micro-groove recording. The technique utilises a signal compression circuit before recording and a matching expansion circuit following readout. Recording is via a logarithmic amplifier based on an operational amplifier circuit associated with a matched (NPN, PNP) pair of transistors connected in parallel, collector to emitter, providing the non-linear characteristics required for the logarithmic operation and the exponential operation of a similar circuit provided for the readout. Bias to the transistor bases is a function of the signal level allowing extension of the technique to very low signal levels.