. The Bell System technical journal . magnetization curve for ironwhich has previously been demagnetized with alternating slope of the first part of the curve is small in either direction ofmagnetization and then increases with increase in the flux and finallybecomes smaller again. Small signals will therefore be recordedweakly and strong signals will be recorded relatively higher. Bothwill have wave form distortion. The same effects would be obtainedwith longitudinal or cross magnetization. In the past, investigatorshave often utilized only one side of the magnetization curve, A d
. The Bell System technical journal . magnetization curve for ironwhich has previously been demagnetized with alternating slope of the first part of the curve is small in either direction ofmagnetization and then increases with increase in the flux and finallybecomes smaller again. Small signals will therefore be recordedweakly and strong signals will be recorded relatively higher. Bothwill have wave form distortion. The same effects would be obtainedwith longitudinal or cross magnetization. In the past, investigatorshave often utilized only one side of the magnetization curve, A directcurrent was used as a bias to bring the recording flux to the mostsuitable part of the curve such as at n, Fig. 5. The method employed here will be made clear from Figs. 6 and the tape elements enter the field of the polarizing pole-pieces Pi, P2(Fig. 6) they are subjected to an increasing magnetizing force. The 172 BELL SYSTEM TECHNICAL JOURNAL Fig. 5—Typical magnetization curve for steel. POLARIZINGPOLES RECORDINGPOLES. LENGTH OF TAPE Fig. 6—Perpendicular magnetization method of recording on steel = Signal coil; P = Polarizing coil; DP = Depolarizing coil. SOUND RECORDING ON MAGNETIC TAPE 173 elements are magnetized to the saturation point P as shown by curve a,Fig. 7. As the elements leave the polarizing field they are subjected toa field of decreasing strength so that the magnetic induction dropsalong the curve b to R, this point being reached when the appliedfield is zero. In Fig. 7, the magnetizing force // refers to the externallyapplied field. The tape elements then pass between the recordingpole-pieces which carry a flux in opposite direction to that of thepolarizing pole-pieces. If there is no signal current present, themagnetic induction will be brought down to the point N by the biasingfield. As the elements pass out from between the pole-pieces, thefield will decrease to zero and the magnetic induction will change from
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
