Musical chords play an essential role, especially in Western music, and the corresponding consonance–dissonance contrasts and emotional continua are still the targets of investigation in psychoacoustics and neurophysiology. In the present study, we define the simplicity of frequency ratios $S_f$ and simplicity of period ratios $S_p$ for the constituents of a chord and propose that those measures should be used as the two coordinate axes in the plane for plotting chords. In this plane, the major and minor chords are reflections of each other with respect to the diagonal $S_f=S_p$. The other chord pair in the same relationship is the major–minor seventh (dominant seventh) and the half-diminished seventh chords. The other triads and seventh chords do not make such pairs of different categories of chords. It was also found that at least for triads, the sum $S_p+S_f$ and the difference $S_p-S_f$ seem to correspond to subjective consonance and the melancholic/sad emotional ratings, respectively. Implications of these findings are discussed. The proposed simple presentation may help interpret and model psychoacoustic and neurophysiological results on musical chords.

和弦起着至关重要的作用，尤其是在西方音乐中，相应的协和-不协和对比和情绪连续性仍然是心理声学和神经生理学研究的目标。在本研究中，我们定义频率比的简单性${\mathrm{小号}}_F$周期比率的简单性${\mathrm{小号}}_p$对于和弦的成分，并建议将这些度量用作绘制和弦的平面中的两个坐标轴。在这个平面上，大三和弦和小三和弦相对于对角线相互映射${\mathrm{小号}}_F={\mathrm{小号}}_p$. 具有相同关系的另一对和弦是大七和弦（属七和弦）和半减七和弦。其他三和弦和七和弦不会组成这样的不同类别和弦对。还发现至少对于三合会，总和${\mathrm{小号}}_p+{\mathrm{小号}}_F$和区别${\mathrm{小号}}_p-{\mathrm{小号}}_F$似乎分别对应于主观和谐和忧郁/悲伤的情绪评级。讨论了这些发现的含义。提议的简单演示可能有助于解释和模拟音乐和弦的心理声学和神经生理学结果。