Vibrato swings upper harmonics more widely than lower ones on a linear frequency scale.

Evidence

That means that the frequency variation in the upper harmonics during vibrato will be greater than that for the lower harmonics when frequency is plotted on a linear scale, as in Figure 5.5. Vibrato often has a delayed start, as in this example. Here, the player makes subtle intonation adjustments to the note before applying full vibrato. This particular bowed violin note has an onset phase of approximately 160 ms and an offset phase of some 250 ms. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1466

Categorization

• DEFINE: Explains why vibrato visibly widens the higher harmonic traces on a spectrogram: the swing is harmonic-number-scaled.