Figure 3

Hilbert spectrum of IMF2, IMF3 and IMF2 + 3. The x-axis shows the time in seconds. The vertical green and red line are as in Figure 2, for visibility reasons the vertical black line of Figure 2 is shown in yellow here. The instantaneous frequency can be seen around 5 Hz. The amplitude of the tremor is color-coded; the colorbar units are dB. The onset of tremor after stopping the bow (vertical red line) and the decrease of amplitude until the bow is taken back to the tip (vertical yellow line) can be clearly seen and is best represented in IMF2 + 3. Higher frequency of low amplitude can be seen when the bow is taken back (between the vertical yellow and green line).