Pitch is the most important auditory perception characteristic of sound with respect to speech intelligibility and music appreciation, and corresponds to a frequency of sound stimulus. However, in some cases, we can perceive virtual pitch, where the corresponding frequency component does not exist in the stimulating sound. This virtual pitch contains a deviation from the de Boer pitch shift formula, which is known as second pitch shift. It has been theoretically suggested that nonlinear dynamics in the cochlea or in the neural network produce a nonlinear resonance with a frequency corresponding to the virtual pitch; however, there is no direct experimental observation to support this theory. The second virtual pitch shift, expressed via basilar membrane nonlinear vibration temporal patterns, and consistent with psychoacoustic experiments, is observed in situ in the cochlea via laser interferometry.

音高是声音在语音清晰度和音乐欣赏方面最重要的听觉感知特征，对应于声音刺激的频率。但是，在某些情况下，我们可以感知到虚拟音高，而刺激声中不存在相应的频率分量。此虚拟音高包含与 de Boer 音高偏移公式的偏差，称为第二音高偏移。理论上，耳蜗或神经网络中的非线性动力学会产生频率对应于虚拟音高的非线性共振。然而，没有直接的实验观察来支持这一理论。第二个虚拟音高偏移，通过基底膜非线性振动时间模式表达，与心理声学实验一致，通过激光干涉测量在耳蜗内原位。