1、1 Scope1.1 This practice specifies the polarity of thesignal on the pin connections from a microphonepresented with a positive pressure on the dia-phragm. It also specifies the resulting positivemagnetization when the positive microphonesignal is recorded on any magnetic media.1.2 This practice also
2、 specifies how this positivemagnetization should be played back and fedthrough a reproducing system to provide a posi-tive sound pressure from the loudspeaker.2 Microphone polarityWhen a positive pressure is applied to the diaphragm,a positive waveform should appear on pin 2 withrespect to pin 3 of
3、an XLR-3-type male connector asprovided on the microphone. (This should not beconfused with either “phantom“ or “T“ remote dc sup-plies used for powering condenser microphones.)3 Audio chain polarityThe audio chain shall preserve correct polarity frominput to output. When an XLR-3-type connector isu
4、sed for input and output, if pin 2 has a positivewaveform at its input, then a positive waveform shouldappear at its output connector on pin 2.4 Recording PolarityThe recording equipment, being fed a positivewaveform on pin 2 at its input, will provide apositive magnetization on the magnetic recordi
5、ngmedium. A positive magnetization is the same direc-tion of magnetic flux flow as that observed in a barmagnet where the flux flows out of the north poleand into the south pole. This flux flow is in thedirection of the physical movement of the magneticsurface.5 Reproduction polarityReproduction of
6、a positive magnetization on themagnetic surface will provide a positive waveform onpin 2 of an XLR-3 connector or the positive terminalof the connector at the output of the magnetic repro-duction equipment (see annex A.1).6 Loudspeaker polarityWhen this positive waveform is fed into the B-chain ofth
7、e reproduction system (the power amplifier andloudspeaker), it should provide a positive movementof the loudspeaker diaphragm towards the audience.Annex A (informative)Additional dataA.1 A bar magnet has an external field with the flux flowingout of the north pole into the south pole (see figure A.1
8、).A recording channel is positive when a positive pulse pro-duces a magnetic flux flow across the recording head gapin the direction of the tape or film movement. A reproducingchannel is positive when a positive magnetization on thetape or film produces a positive pulse at the output (seefigure A.2)
9、.Positive polarity may be simulated in a reproducer bypassing a dc pulse through a wire which is parallel to thereproducing head gap. The dc pulse should be with thePolarity for Analog AudioMagnetic Recordingand ReproductionRevision of RP 134-1986 RP 134-1994SMPTE RECOMMENDED PRACTICEPage 1 of 2 pag
10、esApproved January 12, 1994Copyright 1994 by theSOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS595 W. Hartsdale Ave., White Plains, NY 10607(914) 761-1100REAFFIRMED 2004positive current flow through the wire passing through thepage toward the observer in figure A.3. (This is in accord-ance with t
11、he right-hand flux rule: Grasping the wire with theright hand, the current flow is in the direction of the thumband the flux flow is in the direction of the fingers.)A.2 A practical signal for measuring polarity can be gener-ated in the induction loop by half-wave rectifying a 400-Hzsine wave. When
12、the positive-going half-wave current flowsthrough the conductor up through the page (figure A.3), thisshould produce a positive reading waveform at the output ofthe reproducer.Figure A.1 Flux fieldFigure A.2 Orientation of magnetic head gapsFigure A.3 Polarity measurementRP 134-1994Page 2 of 2 pages
