This paper outlines a method that permits the measurement of the effective recorded stereo modulation axes in test records. Pickup variables are eliminated by the use of a special laboratory single channel pickup, precisely made. A modified turntable is employed which permits tilting of the record surface beneath the pickup, both front to rear; i.e., varying the vertical tracking angle of the pickup; and side to side, when viewed from the front. The method includes measuring the output of the pickup in the crosstalk channel over a -tilt- range of ±10°. The vertical tracking angle of the pickup is set at the -null- of the second harmonic distortion of the test signal. The geometric relationship of the recorded vertical tracking angle to the stylus position and the resulting effective stylus tip motion are analyzed for various recorded vertical tracking angles and stylus positions. Crosstalk -null- curves are measured for a number of commercially available test records, and their effective channel modulation axes are calculated.
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