The Measurement and Subjective Assessment of Modulation Noise in Magnetic Recording
The report describes a satisfactory measuring system in which a meter reading corresponds reasonably well with the assessment of modulation noise by subjective listening tests on various tapes at speeds from 30 ips to 3 3/4 ips. The decision to replace the dc magnetization test by an ac sideband measurement is explained, as are the various parameters included in such measurement. The use of a technique of introducing controlled amounts of modulation noise is described. By this means the threshold of audibility of narrowband modulation nosie is determined both for a 1 kHz tone and for selected musical items as signals, and measurements and subjective assessment of narrowband modulation noise with changes of bias level and tape speed are analyzed. Wideband modulation noise is analyzed in terms of the sidebands produced with and without a pressure pad and/or intertia rollers. This enables a figure of merit for the tape to be obtained relative to a known standard.
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