High Frequency Intermodulation Testing of Stereo Phonograph Pickups
There exists a notable lack of instrumentation and techniques for measuring the total performance of stereophonic phonograph pickups in the frequency range from approximately 7.5 to 20 kHz. The only test that shows promise of yielding significant results at high frequencies is the CCIF intermodulation test in which two closely-spaced tones of equal magnitude are recorded. A number of such tests have been made using a test record on which the primary CCIF tones were 400 Hz apart and glided from a center frequency of 2 kHz to 20 kHz in synchronism with a chart recorder that plotted the magnitude of the difference tone as a function of frequency. The results show the usefulness of this type of test in studying such factors as side thrust, pickup mechanical impedance, stylus-tip size, groove-wall deformation and vertical tracking angle, all at high frequencies.
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