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当一对纯音(40Hz和4KHz)由电唱机重放时,由于机械的非线性作用,产生了4KHz被400Hz频率调制的现象。本文叙述了使用CBS STR-112测试唱片测量400Hz频偏的幅度和相位的方法,说明了FM(调频)的实部和虚部如何从这些数据中计算出来。本文叙述的数字分析,说明循迹角误差只产生实的FM,而循纹误差仅产生虚的FM。这样一来,就有可能从实的和虚的FM数据来推导循迹角和循纹半径。给出的数据证实这种方法能够得到循迹角的精确值。相反,从虚FM数据推导的循纹半径的数值与用光学法所测定的数值差别较大。据推测,此差异可能是由于摩擦拖力引起唱针微小的纵向振动的结果。
When a pair of pure tones (40Hz and 4KHz) are reproduced by the turntable, a phenomenon of 4 kHz generated by the 400 Hz frequency modulation occurs due to the mechanical non-linearity. This article describes how to measure the amplitude and phase of a 400Hz offset using the CBS STR-112 test disc and explains how the real and imaginary parts of FM are calculated from these data. The numerical analysis described in this article shows that the tracking angle error produces only real FM, whereas the tracking error produces only fictitious FM. As a result, it is possible to derive the tracking angle and the tracking radius from real and imaginary FM data. The data presented confirms that this method is able to obtain the exact value of the tracking angle. In contrast, the value of the tracking radius deduced from the virtual FM data greatly differs from the value measured optically. Presumably, this difference may be the result of a slight longitudinal vibration of the stylus due to friction drag.