Three FM-distortion methods for measuring the vertical tracking angles of phono pickups are described and compared. Data from ten pickups verify that the three FM methods give results consistent with each other to within the calibration tolerance of the test records and measuring equipment, which is estimated to be ±5%. In addition, the vertical-angle values obtained by the FM methods agree on the average with angle values obtained by an optical measurement technique. One of the FM methods is particularly suited to production-line testing for quality control because precise measurements of the vertical angle can be obtained in "real time" while a single band on the test record is being played.
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