Is it talking about the phase?¶
Spectrograms usually show the magnitud power of the short time fourier transform (STFT). This is, the color in the spectrograms indicates the intensity for each time frequecy bin.
The missing component in the spectrograms is the phase. The phase has different perceptual correlates. It may affect pitch, the reverberation or other time dependent attributes. Lets visualize the phase with a color wheel to represent the circularity of the phase.
A beautiful serpentlike pattern! Lets make it disappear by choosing a constant phase for every bin and listen to the result.
The voice is now like that of a robot and a strange pitch appear. The spectrogram looks the same, so why? The hop step of the spectrogram is aprox 8 ms, so reseting the phase in every frame introduces a pitch of aprox $1000/8=125$ Hz. Lets make a sweep of the hop step and zero phase, so we can listen the frame rate vary.