Pitch circle is the reference circle from which all transverse spline tooth dimensions are constructed.
节圆是一个参考圆，花键的键齿的所有的横向尺寸都是以节圆为基础开始计算的。
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Sound example 5: "Yankee Doodle" played on strings tuned to the same pitch (transverse frequency) but with different longitudinal mode frequencies (two versions in different keys).