. The Bell System technical journal . PHYSICAL ARRANGEMENT Fig. 3—Method of erasing magnetic recorder. 538 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 5ZJ -40 O-i -\-45 0-65 REPRODUCING SPEEDHEAD - 6 INCHES PER INCHES WIDE INCHESTURNS-1800 \ \ ■ . 1 .- 1 1 1 1 1 , _^ 40 10,000 60 80 100 200 400 600 1000 2000 FREQUENCY IN CYCLES PER SECOND Fig. 4—Typical noise spectrum of i-inch iron oxide impregnated molded neo-prene bands measured in 200 cycle bands after neutralization erase with 60-cycleac field. showing the apphcation of this erase method to a cyhnder-type
. The Bell System technical journal . PHYSICAL ARRANGEMENT Fig. 3—Method of erasing magnetic recorder. 538 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 5ZJ -40 O-i -\-45 0-65 REPRODUCING SPEEDHEAD - 6 INCHES PER INCHES WIDE INCHESTURNS-1800 \ \ ■ . 1 .- 1 1 1 1 1 , _^ 40 10,000 60 80 100 200 400 600 1000 2000 FREQUENCY IN CYCLES PER SECOND Fig. 4—Typical noise spectrum of i-inch iron oxide impregnated molded neo-prene bands measured in 200 cycle bands after neutralization erase with 60-cycleac field. showing the apphcation of this erase method to a cyhnder-type method of erase results in a background noise level measured un-weighted over a 4000-C5^cle band which is at least 45 db below a 1000-cycle signal recorded with 4 per cent total distortion. A typical back-ground noise spectrum is shown in Fig. Fig. 5—General view of recording machines in 3A announcement system atCleveland. NEW RECORDING MEDIUM 539
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